I think we are having two slightly different conversations and its probably my fault for not taking the time to explain properly. I agree with everything you are saying, Im talking about a vague timescale of the next 3-5 years rather than anything happening right now. The key things I can see potentially happening are:

1) Changes to GW IP that either drive away old fans or somehow reduce the amount of new fans / change the current fandom dynamic

2) Changes to tech mainly to do with 3d printing or multi-colour 3d printing. Colour 3d printing is coming eventually to the masses and that is going to be a massive game changer for the whole hobby. It may even result in miniature painting becoming much more of a digital hobby than actually putting paint on brushes (eventually).

3) A new IP comes along, similar to LoTR back in the day in terms of miniature gaming, that either GW can pick up or a competitor which could drastically change the market. I have no idea of what this IP could be but eventually there will be one sooner or later.

4) A big 3rd party comes along who can really exploit any or all of the points above and really shake up the market

5) IP exhaustion – the 40K IP no longer has the draw it once had, maybe due to over saturation in the video game market.

Im not saying that any of these things will happen soon but I do feel it is likely that all of the first 4  will happen eventually and probably in the next 5 years. Number 5 I think has a way to go as we havent had any live action stuff yet, but as Marvel Cinematic Universe and Disney Star Wars have shown even big IPs start to lose interest eventually.

All of the above doesnt mean GW cant or wont survive or even thrive but I think these points would also bring risks for GW and I feel in my gut that these things will occur.