[eqvinox]

Both varied control and power options are really valuable. Power is easy: if it's DC in with a separate brick, please use a common connector :). If it has an integrated power block with an AC input, an alternate DC input would be very nice.

For control… it's really a question of balance. "all the things" sure would be nice, but with a mid 4-digit price I think putting a small fully-open Linux embedded board inside would be awesome. Some existing SBC or SoM is preferable over rolling your own, the latter would just splinter off a separate community for no good reason. Also make sure the embedded system has full control over all functions (there should be enough GPIO & I²C…) and has its own power control. Having it able to actually drive the TV display would be nice (and easy these days) but isn't even the point :).

If you don't stick that in, how about a slot/connector for a Raspberry Pi compute module — or some other reasonably sourceable similar module?

Barring that, RS-232 for control is a bit dated, I'd really expect both an USB device port (control in) and an USB power output, ideally USB-C PD capable, to run some small system off. If you have the pins & functions, please spend the extra $5 and wire up leftover "random" interfaces, e.g. CAN or RS-485. Ethernet without adding a full SBC is kinda "meh", putting together some embedded OS with networking is significant effort for very little return.