I guess Fulham can wait quite a bit longer than even 2 weeks. I would have thought up to 10 days before the game. Enough time to get tickets sent out and received. Fans if pushed on transport, drive down to Cockfosters and get tube in. All you fans with your electric cars can even drive into the centre of London for free and charge up on cheap/free fuel. Btw there is planned maintenance on Earls Court to Wimbledon branch of the District line that weekend.
Fulham will want fans to be aware of requirements before buying, such as vaccinations, tests. I guess this is not known at present.
I don't think clubs wil be able to discriminante based on the covid rate in the post code area of the club. Man United would be funny as their support is scattered wide and far. If away fans are excluded it will have the effect the whole Championship.