IMHO those 4 developers can spend their time working on whatever they choose to and are interested in.
True, but I still think they are wasting their time. Breaking the 4 GB barrier is not the thing that will save eCS (OS/2).
ECS must be usable, today, with the limited software that is already available. It is very quickly becoming unusable because far too many basic things are not working (modern WiFi, Bluetooth, disks larger than 2 TB, WLAN, USB 3,0). If a user needs one, or more, of those features, they must go elsewhere. Once they do that, it is highly unlikely that they will ever come back. 4 knowledgeable programmers could make a huge difference, if they worked on the immediate problems, and put things like breaking the 4 GB barrier on the back burner for a while. If they don't do that, by the time they get the 4GB thing worked out (including making some software that might actually use it), there won't be enough eCS users left to care.
And there is always hardware which is available for longer time. E.g. I'm using at work a board from 2010 which is still available.
The problem with that approach, is that it is impossible to tell what hardware will stay around for a while (the manufacturers would never tell, and if you happen to pick something that has problems, you are stuck with it). It is also not going to help to bring back those who left, or encourage anybody to switch from some other OS. It is bad enough that they have to PAY for eCS, when Linux is free, never mind have to buy an obsolete computer (all computer equipment is obsolete by the time it hits the store shelves), with, possibly, difficult to find peripherals, just to be able to run this expensive option. The main advantage to using a small "supported" hardware base, is that those who really care, can usually spot clearance sales for those devices that actually work.
The only possible way to make a small number of "supported" hardware actually workable, would be to buy a couple of hundred identical systems, put them on the shelf until everything works, then try to sell them preloaded with eCS. That would be financial suicide for anybody who wanted to try it. Apple gets away with it because they buy parts by the thousands, and they have a big team of programmers to get the parts working in a timely manner, so the systems don't sit there for a couple of months, before they can be sold. Most knowledgeable eCS users are very careful about what they buy anyway, but it is usually impossible to determine what does work, and what doesn't work, until you try it. After you try it, it can be difficult, if not impossible, to exchange the device, or return it, so then you need to make the decision about what to do next. Sometimes problems get fixed in short order, but more often, it takes at least 6 months (more typically a year) to get problems fixed. I have noted that problems that don't get fixed within a year, hardly ever get fixed, although it does happen when enough people beat on Mensys.
Virtual machines are also touted as being an option. True, they are, but then the user is presented with the problem of deciding which OS to use for each program. There are a few OS/2 only programs that are cherished by many users, but something like Firefox will be available in the host system, usually more up to date, and with fewer problems, than using Firefox in OS/2. All of those programs that have been ported from the host system, will also work better in the host system. Suddenly, OS/2 becomes a small part of the big picture, and as the user learns more about the host system, they find newer programs that work just as well, so they switch, simply because it is easier than trying to keep a virtual machine going.
IMO, the only answer is to put as many resources as possible, into keeping eCS up to date, and working on as much new hardware as possible. Doing that will prolong the life of the product, but it certainly will not stop it from dying, eventually (all good things come to an end, when something better comes along). If eCS is not kept up to date, it will die faster, simply because it won't be usable. The trick is to make priorities, and don't worry about those things that are not needed immediately. Things like the 4 GB barrier will eventually work their way to the top of the list, if OS/2 survives that long, but ignoring things like modern WiFi, will kill it faster, and that will make working on the 4 GB barrier (and other things like that) entertaining, but a total waste of time.
The only other option, that I can think of, would be for somebody to win a BIG lottery, and turn most of the money over to OS/2 development. Even then, it is unlikely that IBM, or Microsoft, would take on the job, and it would likely take one of them to get it done in a timely manner (not to mention that about half of the money would need to be used for legal fees, to be sure that the job gets done properly).