I think the first step here is to tell us exactly what you currently have, be specific. In point of fact, almost any conventional locomotive can be converted to command operation, I've done them from the really huge to the really tiny. Note that if you have a lot of locomotives, this process could get expensive!
John, please educate me, or at least pin down what I don't understand:
First, no one is saying you can't
convert to command control from conventional, only that there is no modestly priced way to do so as a practical matter, unless the "command control fairy" has blessed you with unlimited funds, equipment, and expertise/guidance. Sure, the track and current power supplies from most conventional layouts likely would suffice for now, but if I understand it correctly, you will also need to acquire several layers of command control equipment with which to send and process the necessary commands, and all of the motive equipment will need to be compatible with that command control system (or can be relegated to run in conventional mode, which sort of defeats the purpose of converting, no?).
Second, from what I've picked up from on-line chatter, the whole array of "command control" systems is in quite a bit of transition, at least in the O scale world, with limited availability of (and very
expensive price tags on!) older versions of the needed hardware, and the newer versions are not only not available, but without even a reliable ETA. So, it's not really a matter of running down to the local hobby shop and plunking down a few bucks for a hand-held controller.
So, let me ask -- can
you buy, for instance, a current box set that will allow one to set up an operating command control system on one's layout (please forgive any mis-use of the proper terms -- I mean anything that will allow remote control of the trains, as the OP envisioned, regardless of the proper nomenclature) at a reasonable price? My limited understanding is that the answer is no -- you need a lot of additional control hardware that is of limited availability, and at a very elevated price even if it is available. Do I have it wrong? I'd love to hear there is a reasonable 'upgrade' path . . . but I'm not holding my breath . . . 😕