[davidgerard]

There have been multiple open source Flash player efforts that get 70% of the way there and stall.

I could surmise reasons, and so could you. But does anyone know the reason?

Is there some common blocker that they all founder on or something?

[bsder]

Erm, because most things get to 70% and then stall?

"The first 90 percent of the code accounts for the first 90 percent of the development time. The remaining 10 percent of the code accounts for the other 90 percent of the development time." —Tom Cargill, Bell Labs

The differences between something having 90% and 99% and 99.9% coverage is GIGANTIC at each step.

[mips_r4300i]

Not an expert at all, but there is a complexity wall when you get to newer Flash with ActionScript (3)?

My very rough guess is that post late-2000s content frequently needs these features and it's at least an order of magnitude work to recreate them

[extraduder_ire]

I think it's more down to engrained quirks in the existing implementation. IIRC, adobe gave mozilla an open-source implementation of actionscript 3 back in the day to try and help legitimize it as an ECMAscript implementation.