As I've said many times before, the reason I don't believe in a federal UK is because England is so much bigger than all the other parts put together that it would need to be split into two or more separate nations for it to work (and each part would need to have its own legal system, NHS, education system and football team in order for federal symmetry to be achieved), but the English clearly don't want to see their nation chopped up any more than the Scots would, so there is no practical way forward.
However, if the Republic of Ireland was willing, I would have nothing against being part of a federal country called the United Celtic Republics. I guess Ireland and Scotland would form it, but I reckon Northern Ireland would join soon afterwards, and I wouldn't be surprised if Wales joined eventually, too.
Crucially, none of the constituent parts would be able to dominate the federal parliament, which together with a proper constitution would be the best way to ensure that the country works for everybody.
One obvious advantage would be that it could inherit Ireland's EU membership, so there wouldn't be any worries on that front.
There might be some disagreement about the location of the federal capital, but there's really only one city that is both Irish and Scottish, so I think Glasgow would be the obvious choice.
Of course I don't really believe the United Celtic Republics will ever be formed, but I honestly think Scotland and the other Celtic nations could all thrive within it. The problem with the UK is that England is far too large compared to the rest, and the lack of a codified constitution makes the situation even worse. It's not being part of a union that makes me fight for Scottish independence, it's being part of an unequal and badly designed one.