There isn't a successor board, not really. But people have started to buy ultra small form factor (USFF) x86 computers and thin clients that got cycled out by corporations and leasing companies, with great success I might add.
The price/performance (+size) is about the same as for the Pi, the power draw is not as bad as with older Intel/AMD machines, and your I/O options and x86 software compatibility is vastly better.
The only drawback is that you're buying used instead of new, and that your starting price for a small home lab (albeit one that starts at 2-3x the power of a single Pi) is larger, which harms students and other makers on a shoestring budget.