Mmm, these might be a nice start, but I don't think they're in the same tier as the OP-1. The appeal for me is the world class integrated visual design and build quality.

Get an Axoloti synth, add your own preferred world class visual design and build quality:

http://www.axoloti.com

My favourite is the Chlorophyll box, which just kicks so much ass:

https://www.filipruisl.com/work/chlorophyll/

The Axoloti looks great! I mainly have the OP-1 to make a chiptune OST, but Axoloti Patcher seems like it would be more functional. What I really want is something that can emulate old gaming console chiptunes and be portable.

I have an Open Pandora which has pretty much every old gaming console onboard. ;). Maybe you can find one - they're amazing machines, or .. get a Pyra, which is an update of the concept by the same folks.

https://openpandora.org

Or, maybe what you want is Anaologue Pocket?

https://www.analogue.co/pocket/

Dunno if its shipping yet though..

Maybe Axoloti is the answer. Its a very nice bit of hardware, I should use mine for things more often...