Totally unsourced conjecture, but there is speculation that the L-TWOO RX 2x12 shifters share the same Shimano 11s Road pull ratios with the R9 2x11 and GR9 1x11. This means that Shimano 11s Road RDs (incl. Tiagra 4700 10s) can potentially be turned into 12s with a pair of L-TWOO 12s shifters.

PSA: Please please please don't buy this groupset if you're price conscious and can't afford to write the purchase off. This is not the product for someone who simply wants something that 'just works' and can't stomach the pain when something goes wrong. The software is barely 1st gen, as is the hardware and everything is subject to change in later revisions/generations. I'm excited in the eRX because the underlying foundation could truly shake up the industry but evidently there is still much to improve.

By the way, zero proper reviews exist on the Chinese side of the internet as everyone there is waiting for someone else to take the risk. Just this week someone posted about aftermarket DM hanger clearance issues. Again, don't be a guinea pig.

Have they said whether the eRX has satellite ports? I’m guessing no. Maybe for the second gen. For me, that’s one of the huge benefits of electronic shifting. And a prerequisite for me to upgrade at this point.

Tires it'd be frame dependent.

I'd be curious if you could use a hanger extender like a Wolftooth Roadlink? The ERX appears to use a similar shadow style hanger setup now, so it could be possible push the RD to clear an 11-40t if it fits.