All points mentioned here are totally valid, however I have another to make...
What C3 needs more than anything, is published games out in the wild.
As someone that's used Construct since the Construct Classic days, I've routinely checked out other engines (as they all have shortcomings, and sometimes C3 hits me with a wall I can't work around), and the FIRST thing I ask myself when investigating any other engines is: what has been made with it?
If I don't recognize the name of at least ONE game listed, generally I move on, not out of spite or anything, but out of a reaction of: it must not a capable tool, or no one else is using it either...
Examples won't get anyone's attention, neither really will demos... only finished and sold games will, I'm afraid.
While not aware of Scirra's financial situation, what would really help to ship games, would be to either offer or partner with a publishing service, especially if its capable of helping devs to completion, be it through direct tool support, project funding, distribution, etc...
If there are few to no visible games in the wild, then the engine isn't visible either... and that sucks, because Construct 3 is awesome.
Is the cost to entry high for young, new, solo devs? As someone in Canada, yes, I have to justify my monthly subscription to my wife every month, as C3 still has yet to bring in any revenue to our household to justify my continued use of it.
Are there features that newcomers will be looking for that aren't in place yet? Of course there are. Whether or not those are in the pipeline or never intended is unknown, but they will be viewed as "currently missing".
Does that mean the tool is no good? Absolutely not, C3 is fantastic. But no one knows about it when there are no tangible and visible projects made with it. MIGHTY GOOSE is probably the most well-known/obvious title that we can all point to, which is a great start, but there needs to be more.
So my point is, whatever can facilitate more finished games of quality and polish, getting out the door, and making a little money, in app-stores, e-shops, Steam, Switch, PlayStation Store, Xbox, whatever, is what NEEDS to happen.