It'd have been very good, with it probably getting a DQ ending, since in like 97 or 98, no way in hell would they have him tap out to Bret, and they probably wouldn't have given a clean ending. Could see Bret trying to get a Sharpshooter on but Kane choking Bret and not letting go before the 5 count, or some Foundation shenanigans.
1998 Undertaker had four amazing matches at Royal Rumble, Unforgiven, King of the Ring and Summerslam (ok this isn't quite amazing but it's better than could have been after Austins concussion - thanks to Undertaker carrying it) .
I can't recall Kane having that many great matches and most of his best ones all involved Undertaker.
Back to the OP, fantasy booking Kane and Bret into a match at Summerslam 98 would have been a great way to legitimise Kane as a serious main event star (he was already by this point but having a match against Bret at MSG certainly wouldn't hurt).