Eagle is the hobbyist standard today because it was free for small simple stuff a decade ago.
Eagle is not the hobbyist standard for any other reason. Momentum was gained by Cadsoft because there weren't any other free, good tools. When the "maker movement" started lots of blogs suggested eagle precisely because it was free, and often the blogger shared their design files.
The mechanism of sharing does not concern me, so long as sharing is possible.
Other communities use adf.ly to share their files, and I'd love to see that die. If I don't have to pay to host stuff I wanna create, I'm onboard.
CircuitMaker does not need to cater to Eagle customers; that should not be the immediate goal. CircuitMaker needs to attract people who would have otherwise chosen eagle tomorrow, first, THEN attract existing eagle freebie users. This is what makes the new UI such a smart move.
I have eagle and I use it often.
I want to see a genuine competitor. CM has a very good shot.