Having stadiums bid for matches and just holding the semi finals and final in one stadium might be the way to go since not many countries have the facilities to host a 24 team tournament.
I was wondering if it might pave the way for more joint bids. Either 'equal partner' type bids like (and I know they've done it before) Belgium and the Netherlands, or possibly 'senior and junior' pairs which might be a way for smaller countries to be part of hosting an event that they couldn't bid for outright, so maybe Germany & Denmark, Italy & Switzerland, Poland & Lithuania etc. with an unequal share of games, but both qualifying as host.
Both Switzerland and Poland have already co-hosted Euro finals. Not sure Lithuania has even one stadium suitable for Euro finals matches, the stadium where England played there was described as a 'non-league ground'.