One reason why inductive breaking (Wirbelstrombremse) is only allowed on "feste Fahrbahn" (ballast less track) for Germany's high speed ICE (inter City express) trains, at least as a service brake.

On some ballasted track they're allowed for emergency breaking ("Schnellbremsung"), as they can interfere with equipment like axle counters.

This is done because they have to wait for the track to cool before they are able to safely drive on it after it got heated.

These are btw just a linear induction motor with the field coils locked to standstill.

I have since wondered about using this for traction, as it's likely not too efficient but ought to have potential for a much simpler drive train, using much longer parts of rail under the vehicle to get the desired force with a low slip (and thus low rail heating).

Say, for vehicles that don't normally need (this much) acceleration, and would thus prefer few/no driven axles.

We are at a point where power electronics are cheaper than some traditional transformer technology, and being able to deliver high accelerations (on the order of 3~6 m/s²) near zero speed to regional trains could vastly improve their average speed.

Just make the people have a wall/backrest and those forces are harmless.
Turn them around for the next stop if you want to brake that quickly or use it to catch up a small train car to a full trai;, have two stories, walkway backwards on top, forwards bottom, and drop the tail off from the through train after it has exchanged people.
Don't need seats there, just walls at, like, shoulder width pitch, to let people stand with their back in the right direction.

If only track pairs were more cleanly parallel, you could just have bridges and let people transfer to and from the fast through train using a local access facilitator train.
That in particular would also let you catch a connecting train without either of them slowing down (a lot) to provide this opportunity, which might even be the bigger benefit.

Sadly trains take ages to board lengthwise as European track clearance gauge doesn't allow for two proper unidirectional lanes of people traffic with decent cross section left for seating, so you'd have to spread the arrival/departure shuttles between front and back for a single dominant people traffic direction (from arrival seat to their transit seat and onwards to their departure seat).

I guess you could work around by using distinct small shuttles that maybe briefly combine for aerodynamics, in relative breaking distance w.r.t. service brakes, and respond to a switch that doesn't reach a safe locked end position by unfolding wave breaker barricades into the gangway (articulated so that they naturally support people leaning against them due to deceleration forces, so they get kinda pushed into place by people using them) and alerting passengers about the imminent rapid coordinated deceleration.
A couple seconds notice should suffice to let people move to hold onto their stuff that'd otherwise go flying from a G of deceleration.

Coming to a stop from 300km/h takes 2.3km (27.8s of travel) at 1.5m/s² (the AFAIK limit for normal standard train carriages to match how the passengers behave), but at 10m/s² it only takes 247m (4.2s of travel).

This would be the minimum dead space/time to stop safely in case a switch fails to transition. Regroup convoys between branching points a bit, and you could run at current-day capacity levels despite most carriages not stopping at any given station (the others just skip past as they didn't branch off).

Honestly I still wonder if suspension rail system Eugen-Langen isn't better for high speed people transport due to the severe passive tilt capability (+-15° in production for a century; +-30° tested (the production deployment wasn't authorized to anywhere near it's tilt angle speed limit for many years, and the frequent stops/stations didn't make that angle look restrictive for the technology at the time: the track isn't even banked as far as I know!)), especially because you don't typically want to share track between high speed people transport and generic mainline rail traffic.

Not needing the extensive tunneling/wide-span bridging ought to make the track suspension requirement worthwhile...
Particularly with how cheap we can make steel truss sections in automated factories, and e.g. sling it under the track for transport to installation site.
Drop it for the irregular junction areas, and just put cheap normal rail to wheel the segments across the junction.

Roller coaster technology has made the needed fast track switches a proven technology, too. (It's really similar to a suspension rollercoaster just with motors and an electric "3rd" rail.)

I for one can't wait for full ETCS Level 3 to become a thing used in production.