Yeah, 2026 is using 16 stadiums across North America with a minimum capacity of 40k. If we stuck with 16 you could have something like this:
SCOTLAND:
(Possibly redeveloped) Hampden Park, Glasgow
Murrayfield Stadium, Edinburgh
WALES:
Millenium Stadium, Cardiff
IRELAND:
Lansdowne Road, Dublin
Redeveloped Windsor Park, Belfast
ENGLAND:
Wembley Stadium, London
Old Trafford, Manchester
Anfield, Liverpool (or New Everton Stadium)
St James' Park, Newcastle
Villa Park, Birmingham
Hillsbrough, Sheffield (very minor expansion/reconfiguration needed)
Elland Road, Leeds (very minor expansion/reconfiguration needed)
Expanded King Power Stadium, Leicester
New Bristol City Stadium, Bristol
Expanded Stadium:MK, Milton Keynes
Expanded Home Park, Plymouth
All of those English venues were part of the England 2018 bid except Leicester - they had a new ground in Nottingham instead, but Forest redeveloped the City Ground while Leicester have obviously come to prominence in the same region and are already seeking planning permission to expand their ground. It gives a good geographical spread and they're still all very good venues. It also means you have big grounds elsewhere from Manchester to Sunderland to London as very capable backup venues if any of the construction projects go wrong.