I made some similar to the BFS fish head for 135mm. The iso tab is easy with 135mm because it is on the same plane as the dropout face, just get something lasercut with the iso tab built in. Things get more complicated if you wanted to do thru axle hubs as the iso face is offset to the drop out face, Learned that one the hard way and had to cut it off and re-attach!
I do wonder if a steel thru axle with a nut at the other end could work with a slotted dropout. I guess the hub ends may be an issue as they are usually aluminium and may get smooshed.
I had a Stooge mk4 a while back with an eccentric BB, it was trouble free. I think I may have saved myself potential issues with it as I pulled it apart and greased it before assembling the bike. it was an aluminium centre in a steel shell and it could get galvanic corrosion issues with a lot of weather exposure I imagine.