Honestly, there will have to be the ability to grandfather in older non-compliant drones. Even if there is a "retrofit" add-on available, it would have to integrate into the systems to glean the information needed, and if it doesn't integrate that is just a whole lot of electronics to add as a "retrofit" which would basically eliminate a lot of smaller drones (
MM1/
MM2/
MA1/
MA2)... Might even preclude the MP1/
MP2 series as well.
Honestly, I think our older, non-compliant drones will go as follows: (and this route would basically make all existing non-compliant drones even more valuable)
a) They will require full registration of each non-compliant drone via serial number. If you don't get them registered they are considered "illegal to fly". Basically, that is just to be sure that if you end up causing an accident you are held accountable.
b) You cannot sell or transfer a drone without it being approved. Heck, they may not even allow sales of drones if they are registered to an owner. Doubtful, but they would have to have some way to verify that a non-compliant drone is owned by someone new, and the original owner would have to be motivated to inform the FAA of the transfer, lest they be held accountable if a disaster happens.
c) For these legacy drones they may even require a remote "kill" or "return-to-home" that can be activated via law enforcement or some other authority to force them out of the air as a "last resort". Again, hard to enforce and basically just as questionable as adding telemetry payloads as auxillary devices to existing non-compliant models.
If that doesn't happen, then they may just ground all non-compliant drones as just that, non-compliant and not-able to be flown.
In either case, it is obvious that they are in full "nanny" mode, wanting to be able to identify who is doing what in our shared airspace. Not that I blame them, but totally kills the idea of a drones being "fun". Imagine if they did the same thing to quads or dirt-bikes that are ridden off-road. It wouldn't be anywhere near as fun. Again, not saying that is such a bad thing, since it is obvious (by the pure amount of totally ridiculous youtube posts by irresponsible drone pilots show alone) that "people" in general cannot be trusted.,
It does make getting into drones as a business a much steeper slope. Regardless of what people say, but I bet a whole lot of people that ended up getting 107 licenses and are doing drones commercially for profit started out with just a recreational (or even no FAA registration at all) to begin with. I know at least a dozen or so people that are doing it that got in like that. After they knew it was profitable, or a drone loss or a liability "close-call" they all wizened up and got their 107s as well as proper insurance coverage. A few even used that as the benchmark to deciding that they couldn't make it a viable enough business to support their families and went job hunting. Point being that it is obvious that there is a now a "wall of admission" being established to getting into drones commercially that was always there under the guise of "you had better not get caught without" situation that is now going to be a firm "you WILL get caught" if you don't.
Again, I am sure that the big issue here is not the drone enthusiasts, but the irresponsible drone "wanna-be" that wants to get more likes and views online, as well as a healthy push from big dollar interests such as Amazon and others that want to get into drones for commercial interests. Too bad the rest of us are getting caught in the middle, since we are the ones that allowed companies like DJI to get as big as they are to have the opportunities they have, which usually means we are also the ones to pay the price for their success by being left-behind and disregarded. Just look at all the early Apple adopters. Basically "fools every one" viewed by Apple for making them successful.