That's possible, but let's look at more possibilities.
They could wait for 11.3 to be released, test a bit longer, as you say.
But if they've already been testing the beta enough, they may not feel they need to test it even more after it is released.
Or they could feel it is "good enough" even if all the bugs aren't fixed. After all, it is a pretty big deal with Apple already solving half of them. Remember, WT has never said they are trying for perfection (they've said quite the opposite). But many people think that's what they are doing out of frustration.
Heck, they could feel it is "good enough" already and are doing final testing.
Of course, we don't know if there is anything else causing delays. Would really be nice to know!
As for only shipping to iOS users, that's possible too, but I doubt it. For one thing, it would really screw up people's position in line. Some are already angry about testers "jumping the line". I disagree with that and would have whether I was selected or not - because when this Treg thing was first announced, I didn't even sign up because I thought they would be focusing on people with nice computer related credentials. Yet I wasn't upset that people would be selected ahead of me. I just wanted them out of WT offices and to other people to get their views. It could be done the same way as keycaps for different layouts. They said they send out emails telling people what was available at the time and how long to get a Dvorak, colemak, etc version out and the customer could decide whether to wait or just take a qwerty. They could add in that the android app isn't ready for X number of weeks and ask if they want it shipped anyway. But I have a hard time seeing them just saying android users simply can't have theirs at all when shipping starts.
Anyway, besides that, we do have people testing on Android (and windows and Linux, etc). Maybe a minority so hard to compare the numbers of complaints, but I haven't seen any trend in problems with those for some time (again, I only have limited information from Slack reports).
Now, I wouldn't be surprised if orders for android, etc, were made without an app yet - it would still work as if it was a standard keyboard (but better!) until it was ready. WT said long ago that it would be 30 days or so after iOS app was done. Where they draw the line on "done", I do not know since, certainly, there will be regular improvements to it.
OTOH, since this was said so long ago, it is possible they've been working on it for quite awhile so it could be ready sooner than that or even when they ship. So this is another thing WT could update us on.
One more thing, the list I keep of persistent problems individuals have reported is the smallest I've seen and, as before, over half of those have not updated their experiences in at least 7 months! Of those with these issues, the most recent report confirming it was in January.
But keep in mind there can be issues that I don't list as "persistent". If someone reports a connection problem, I don't count it unless it keeps happening. It can be rare, but can't just happen once or twice over a long period.