All the workarounds proposed have a significant development effort associated with them, while the chances to return the investments are pretty unclear. Talking about workarounds, I would not hold my breath too much.

I could partly activate the internal routing by setting rules but it still worked only partly. Exporting to a RSC file does not complete and the last complete section is: /ip service and the next service /system time is not present in the file and also the rest of the export. The nexthop in routing displays all unreachable, manually removed the double main next to default dynamic main and the blank one. Update 2: hanging in there like a pit-bull I tried again. Looking forward to try 7.1Beta4 somewhere in 2021. All my internal routing was also dead so no in fun testing this way. My external IP I could not set as preferred source on my PPPoE connection or I had to make my own static routing entry. After I corrected all the changed routing marks it still not work and I could only ping/traceroute directly from the router to 8.8.8.8. Both worked but it is confusing this way. Routing was changed (expected), routing labels where set main and when I wanted to traceroute there where two routing tables main in the list. The PPPoE dropped back to 1480 and manually I could set it to 1492 to a bit be closer to the 1500 that I can use in 6.48. Update: I could change de MTU but sadly not the one I wanted to. Hope this will also stop the router crashing when you change the MTU of an interface.

Routeros 7 beta