As a Scot would be great to get a world cup bid like this together and would have good chance of success. Need the fa and SFA etc around the table. UK bid great but feel trying to add Ireland not such a good idea and feel having too many hosts could weaken bid anyway as too many would be already qualified then as hosts. FIFA seems happy with 3way bids now,so nice as Aviva stadium is don't think there is any need to have joint bid with ROI. NI as part of UK would be nice to include but no stadiums suitable as usually to be over 30-40000 capacity minimum.
A three way bid England Scotland Wales all on one island could be very successful. No requirement for fans to ferry etc to Ireland then as FIFA supposed to also consider things like travel links etc required for fans getting to venues.
Not too many in one city either,know from Scotland's failed euro 2008 bid the preference with these things is not too many in one city,in euro 2016 Paris got away with 2, (a world cup is obviously slightly different), think 2-3 in London max, probably 3-definitely Wembley and maybe another 2 probably including quite iconic former Olympic stadium that's now west hams and any one other of London's, probably just 2 in Glasgow-Hampden as national stadium (52000) and Celtic park as biggest (60800). Scotland could also supply murrayfield at capacity of 67000 in Edinburgh-Murrayfield is biggest stadium in Scotland and has hosted plenty big football matches successfully (Liverpool playing Napoli there this summer) and it also has decent transport links now with it's own stop on the new Edinburgh tram network which links to several railway stations and Edinburgh airport also.
Obviously Wembley for the World Cup Final, Semi Finals require 60000 capacity minimum,I'd envision Old Trafford for one and the other possibly in either Cardiff or my preference Scotland (since Scotland second biggest contributor of stadiums host!) and both of either Celtic park or Murrayfield are big enough for one semi final in Scotland-(hampden is not). . So Hampden (52000), Murrayfield (67000), Celtic park (60000), obviously Wales the millennium stadium (74500), and the rest in England such as Wembley,Olympic Stadium,1 other London,Old Trafford,Anfield,Villa Park,St James Park, Stadium of Light.
Obviously England the largest of 3 hosts and as biggest partner would deserve opening ceremony and final to be at Wembley,in fact only Wembley big enough for final anyway, although if FIFA insisted on opening ceremony being in another host nation them Hampden or Millennium stadium for opening ceremony and Wembley for Final-but Wembley for both would make most sense really if allowed. Finally consider both 2030 and 2034 as Uruguay etc joint bid might for 2030 might carry weight that year to mark 100 year anniversary of first world cup in Uruguay in 1930. If looking that way then 2034 maybe for UK. Either way long way away!
Also some infrastructure improvements to go with it,like finish the dualling of A1 all the way for example as it links Edinburgh venue to Newcastle venue etc. Sure there are plenty similar infrastructure improvements that could be really useful across England and Wales too that would also help with the bid.