I think that this is a pretty good compromise between what the FAA originally proposed and what commenters said back to them during the comment period. They removed the requirement to be on an internet connection and send info over the internet to a (cost extra) company that would collect that and send to FAA. Instead, these new Remote ID radios will broadcast over unlicensed spectrum (WiFi or Bluetooth most likely). Only the FAA will have the ability to match up the units ID number with the registration database, so there is some privacy there (since anyone with a receiver and app will be able to view where the drones are flying -- just not who they are).
There is a retrofit for us Spark flyers in the form of a broadcast module that can be affixed to the unit. Yeah, more weight on it, so it will likely affect performance, but at least we will have an option for older units to keep flying legally.
If you cannot use built-in (upgrade S/W) system and cannot/don't want to affix a module to the unit, you can still fly but only in approved locations (which will be in an FAA database if you want to find them).
The "broadcast module" units that will have to be affixed to non-compatible drones will have to send lat/long, altitude/time info so they may actually be pretty small since they will need a Wifi/Bluetooth transmitter & a GPS chip to get their location , speed, and time data. That's just a couple of chips on a typical smartphone these days. Add a couple of button
batteries or a small phone-type
battery (rechargeable) and I suspect they'll be only a few ounces. With all the smartphones and GPS and Bluetooth/WiFi chips out there the chips are cheap so cost isn't going to be huge either.