Returning from 2+ year break

[MiRai]

To quote myself:

"There is no reason¹ not to have all of your WoW accounts on the same BNet account."

¹there might be a reason, but it's highly subjective

Maybe merging them onto two accounts? To both spread the mounts coverage, and to leave room in case i want to 10-box later on?

Sure, you could do that, but I think the problem is... How will you know which accounts have what prior to logging them in to see? What if you guess wrong and a rare mount ends up on the second BNet account when you wanted it on the first?

Guess it comes down to how much hassle is logging the accounts all at once.

There is no hassle whatsoever.