Some have suggested that the final line is a taunt from Lucifer: "Stay, coward!". This is a case of a neat explanation overtaking the evidence - the pattern of syllables/phenomes plainly doesn't match 'coward', so that idea can be dismissed immediately.
Anyway, we now have an 'official statement' of the lyric. The only remaining problem is its meaning...
In the 1999 discussion, Ian told Andy Jackson that the line might have been a reference to two journalists; he was either being coy, or wasn't certain, as it may have been Jeffrey's idea.
However, Ian has always shown a marked reluctance to explain Tull lyrics, and his responses to enquiries, especially in media interviews, have sometimes been... misleading. A footnote to 'Solitaire' in the official lyrics book identifies 'Steve', but another footnote claims that Magus Perdé was a genuine medieval person, which is extremely doubtful. Without corroboration, I feel the 'two journalists' explanation is still open to speculation.
Let's take this in stages:
An alternative might be 'Steve' isn't specifically Peacock - rather than attack any real person, Ian/Jeffrey referred to a fictitious, generic critic and just happened to name him 'Steve'. This is a bit too easy an explanation. In the context of 'Solitaire', it might work - the whole song sets the scene, and the precise name given to the critic in the final line doesn't really matter. However, if Ian/Jeffrey hoped to be able to distill 'Solitaire' into one obscure line - and still have the audience understand - Steve must have been a real person, well-known to be an opponent of Tull.
- It's probably safe to assume that this was the same 'Steve' as was named at the end of 'Solitaire', written during essentially the same period as The Play. Having dropped 'Solitaire' from the finished album, Ian/Jeffrey may have wanted to slip in the reference anyway.
- It is also fairly safe to assume that 'Steve' was indeed a music critic who had given a rather poor review of a Tull album or show - that's the central point of 'Solitaire'.
- The only significant music critic named Steve (at least the only one remembered today), to whom Ian might have been referring was Steve Peacock, of Sounds magazine. According to the official lyrics book, Peacock was 'Steve' in 'Solitaire.
- Peacock did indeed write a distinctly hostile article, highlighting the lack of spontaneity in Tull's stage show (the central point of 'Solitaire'), published in the 11 March 1972 issue. Beginning "One of the most disillusioning experiences of my musical life...", the full text of the piece is available from Tullpress, here.
John Brett suggests that the other journalist may have been Caroline Boucher, who had interviewed Ian in 1969, but I'm not aware of a reason for him to have singled her out for especial mention years later.
There is a theory about Caroline, which I may have formulated myself some years ago. Though hopefully of interest, there's no proof whatsoever that it's correct!
Starting in the Sixties, a number of pirate radio stations managed to evade regulations by broadcasting from ships in the English Channel, the most famous being Radio Caroline. Several major UK DJs started their careers on the station, which played pop music not otherwise covered by the mainstream stations; Caroline was founded before Britain had commercial music stations or BBC Radio 1.
By 1972, the mainstream pop stations were well-established, so Caroline switched to broadcasting only album tracks (not least because album sales far exceeded those of singles). The taste of Caroline DJs tended to reject most 'pop derived' album material, so, as the 'official' history of Caroline explains:
...Caroline listeners could expect Led Zeppelin, Eric Clapton, Jethro Tull, Yes, Lynrd Skynrd, Barclay James Harvest and so forth, together with suitable Dutch bands, such as Golden Earring and Kayak. It is difficult to put into print the spell woven by this music when blended by the determined exiles on the ship...
It is reasonable to assume that this means Radio Caroline broadcasted significant sections of 'Thick As A Brick'; probably the only British station to do so. Even at the time they were recording The Play, Tull must have realised the album would receive limited radio airplay (in 3- or 4-minute segments, at best), but could rely on Caroline to give it reasonable coverage.
So, as I understand it, "Steve! Caroline!" means "**** you, Steve. Our real audience listens to independent music stations like Radio Caroline, not mainstream/establishment critics like you."
This would be a more reliable explanation if there had been a mainstream radio DJ who'd publicly criticised Tull; it would be credible for Tull to be saying "you criticised us on air and won't play the record, but Radio Caroline is better anyway".
However (as you've guessed), I haven't been able to identify any such individual....
Another idea proposed in TalkTull by, er... me, was an attempt to explain why Ronnie seems so unmoved by his experience in the afterlife:
Or is there something we're missing in the "Steve! Caroline!" line? Could
Ronnie be excitedly calling to his friends: "Hey, Steve! Listen to this,
Caroline! You're not going to believe the dream I just had!" This might
turn Ronnie into something of an Ancient Mariner character.
Carsten Bergmann sees Steve and Caroline as merely other 'everyman' people returning to life at the same time as Ronnie.
A key point is that I don't regard this final line to be part of The Play at all - it's tacked onto the end of the album after the Play itself has ended (and the notional theatre audience are gathering their coats).
It does seem an extremely odd way to end the piece - after a weighty journey through death, limbo, judgement, heaven, hell and resurrection, why conclude with a petty swipe at the critics?
Could it be a distancing tactic; Ian attempting to dissociate himself from the idea of being too 'serious'? Similarly, in 1975, 'Baker St. Muse' ended with a joke about being locked in the studio; possibly a mock apology about the unfashionable length of that song.