The answer to your question may well be what Cirrus is willing to do on a customer by customer basis.
The short answer, at the moment, is “not much”. Cirrus will only deliver what has been certified, they don’t do custom mods.
The background to the engine monitoring is that Arnav have the inputs built into the MFD to accept all the sensors needed for full engine monitoring, and the fuel flow sensor is already there. Extra CHT and EGT probes are needed, but the firewall connector for this is there, with pins reserved.
The missing link is the software; Arnav have engine monitoring software for their smaller displays, but it is still not working for the large display. Cirrus originally told Arnav they didn’t like their (Arnav’s) monitoring software, and would do their own for the SR20. Of course, this never even got started, so by the time the SR20 was ready to sell, neither Arnav nor Cirrus had the software.
I believe Arnav are working on it now (and Cirrus have abandoned their plans to get involved). At some point in the (hopefully not too distant) future, a software upgrade will become available for the Arnav that, along with fitting of the EGT and CHT sensors, and some wiring, will give you full engine monitoring on the Arnav display.
As far as Skywatch, TCAD or whatever, I have no doubt this will come, but when I don’t know. In the meantime, a lot more people get killed by weather and fuel exhaustion than mid-airs (but I accept that the threat of a mid-air is scarier, simply because you have less control over it).