The reason that there is no Scottish or Welsh culture is quite simple there were no large scale Scots or Welsh national uprising during the period (unlike the Irish say). So therefore if we did add these cultures we need to give them to Britian. No one else has the nack for ruling British pops so all we would do is create two new culture tags give them to Britain and there would be no change in the game. The effort required for the pay off is well just not worth it in my opinion.