First 2 points are pretty valid but would obviously fall under potentially a bit more expensive to obtain vs difficulty in obtaining at all, though if I've misunderstood your sentiment I'll chalk that up to the internet. I've honestly not heard any mention anywhere of any ban or restriction of European stores selling anything airsoft related to UK customers though, so again I'd maintain the a concern over difficulty in purchase wouldn't really be worth too much worry (speaking generally here). I mean it's possible for some guy in Poland or wherever to suddenly get the made-up notion that they can't ship to the UK anymore, that is a possibility I'm quite open to that notion, but it seems an incredibly slim possibility. Especially given that European airsoft/gear shops probably get a ton of business from the UK so if there is no legal restriction preventing them conducting said business they're not going to shoot themselves in the foot.
I'm saying this more for the sake of the lurkers btw (of which there are a great many) because brexit is obviously a mess in terms of how everyone in power has handled it and given the confusion level already existent I think the potential for inaccurate rumours to spring up is very high at the moment. That will probably only get worse in the next few weeks as well given the constant votes in parliament that are going on and the rapidly incoming leave date (maybe..).