If all EU start to accept bitcoins demand for bitcoin will increase a lot. First there is not enough coins for everyone, price can be 10k, 20 k, that is ok but that will not be affordable to many EU citizens. If this happen which altcoin will be behind bitcoin? Bitcoin will be first, most expensive coin that is certain, because of that much more interesting is who will be behind, which altcoin can follow this and which coin can worth 1000 $ when bitcoin will cost 20 k?
They will not necessarily need to buy a full bitcoin, they could buy a fraction of it, besides if something like that happen I think we could see a huge bubble forming since very soon people will realize they can buy a bitcoin for a price and then resell at bigger price at a later time.