Personally I think starting a new club while the old one stands is pointless. Not only are owners likely to move on at some stage, but it handicaps a new club as the old one still exists, and some will follow it regardless.
Negative? Maybe, but I think it's positive to make sure peoples' effort isn't wasted. If it doesn't succeed, it then gives added strength to the current owners who would have seen off a challenge, and so have their own position strengthened as a result. It could actually work in reverse of what's hoped for.
If the club dies or moves out of the city permanently, that's when a new club should start. This also helps in that there would be no challenges from the current club for use of a similar name/ similar colours etc. all unhelpful things that could stymie a new club before it even got off the ground... and many people wouldn't follow such a thing unless it looked the same as 'Coventry City'. To give it the best chance of succeeding it needs to maximise its potential and minimise its costs; that only happens when/if the old club dies or moves out of the city permanently.
If the club dies, a new club shouldn't be in the Ricoh. The Butts is the obvious place to start with, but a smaller stadium is a must to keep those costs down. It needs to give itself the best chance of success by keeping its costs down. After all, a new club would have a fan base far in excess of its immediate competitors, so why waste that money advantage by spending it needlessly elsewhere? We don't have to be welded to the Ricoh, we have to be welded to Coventry. The Ricoh can wait until a club is big enough to make best use of it and, if the Ricoh falls in the meantime, the Butts could be developed up to a certain level organically, with temporary seating, until the club was in a position to outgrow it and demand a stadium on its terms, in its city... not on the terms of a council, or an anonymous investment fund.
That way, the club gets momentum and its money advantage and can progress quickly.
The more constructive action at the moment, in my opinion, is to push SISU to actually nail down their plans. If they actually built a stadium in a suitable place that'd be OK. They won't of course, and they won't be able to prove that they intend to, but instead of targetting blindly the 'no to SISU' it needs to be asked 'no to what?'
It's not 'no to a club owning its own ground in the city'
It's 'no to owners using misleading statements to try and fracture a fanbase so they all give up'
So... assume they are telling the truth, the burden is on them to show they are telling the truth and this should be simple. If (and it's a big if!) they are, then a lot of the issues with them go away anyway. The club can live in the city, and own its own ground again.
What's more likely is there's a cat-in-hell's chance of them proving that, so the way to unite fans is to have them go along to these forums and demand to see the actual plans, the contracts signed with builders... everything physical. Continue to out them, continue to back them into a corner.
And if, when backing them into a corner, the result is the club dies... that's when a new club can be formed, at which stage it will get far more support, will be something to unite the fans around, not divide them.