I don’t get the need to share the hosting with another country, or countries? There are plenty of big enough and good enough stadiums in England. They surely can’t still going by the old rule of a maximum of 2 stadiums per City which rules out at least 2 or 3 in London?
Ireland and Scotland have probably 2 each (and I’m not including Hampden in that as it’s a shithole) and there is only really the Principality stadium in Wales.
48 team tournament, and the minimum stadium capacity is 40,000, 12 seems to be the normal requirement in previous tournaments however Qatar got away with 8, but those were 32 team tournaments.
A total of 11 stadiums in England meet the 40,000 requirement, but 5 of those are in London so for public safety reasons you'd probably need to exclude 2 or 3 of those, Goodison, Hillsborough and Elland Road are close enough that you could probably expand them slightly and meet the requirement so at a push, if we allow 3 from London, we could probably supply 12 stadiums of the required size.
The bigger problem might be training facilities, you need 24 venue specific sites, plus 48 team specific sites for a total of 72, so if you simply took the PL and EFL club's facilities you'd have to go down to L2 to find enough, and with the best will in the world I don't think the FA would be entirely comfortable putting forward Squires Gate as a potential base for a world cup squad. You could probably rope in some facilities from other sports and elsewhere but it's going to be a push.
Potentially I think England could do it alone, but it'd need some considerable investment to get everything up to scratch and I think the funding would be hard to get in place, and even then the bid would be marginal, the joint bid gives us an extra 4 - 6 major stadiums plus training facilities as well.
