I have a feeling Digital Foundry will take a good look at this one, but even if not, SwitchUp will for sure, and they do a good job covering the technical aspects of Switch games. I suspect that getting Arkham Knight to a locked 30fps is off the table, but if there are able to smooth out some of the more sporadic minor dips, it will go a long way in making it feel smooth "most" of the time. I would be curious if a 20fps cap when in the Batmobile might actually make it appear smoother because of a consistent update? It wouldn't be ideal of course, but if the framerate is going to hover between the low to mid 20's, a locked 20fps would probably be better. None of the impossible ports have been rock solid, and this is no exception.
At least from the video I have watched so far, Arkham City looks like it got the better upgrade compared to Asylum. Not that Asylum looks bad, but City certainly looks to have better textures than the original release on 360/PS3. Just from looking at aliasing differences, you can tell the Switch builds are higher res than 360/PS3, but cant tell if they got all the way to 1080p or if its 900p.