I keep seeing folks saying they'd be happy to purchase Sailfish OS for 100€.

100€ is around 138 USD. For 40 USD more, I can get an unlocked, brand new 8GB Motorola Moto G. No way I'm paying 100€ for just an OS on an older Android phone. Just doesn't make sense.

They've differentiated themselves via a different OS (MeeGo based) and with a closed source UI. Fine. They've chatted up a way to install on existing Android phones. Great. I don't see that adding to their numbers because so far, the native apps are far and few in-between and they're slightly (at this moment) dependent on the Android compatibility layer.

That last bit straddles the line of "should I wait for Jolla to be available in my area/market" or "should I get an Android phone instead"... and having an installable OS cost as much as I can get a higher spec'd phone (arguable), then I'm going the higher specification route for slightly more expensive and full-on support.

Jolla needs to discuss not installations, but how will it be supported. And how this adds to their efforts.

Don't get me wrong, Jolla's future is bright if you were to ask me. This whole installable Android part is where I'm sorta misunderstanding what they're trying to attempt.

Future implies waiting. So let's wait and see. The rest is speculation unless it comes from Jolla. That's my take...