This is the first change I find I need to throw my voice out there with.
This game already has a very limited community of artists and animators. This game's look and feel DEPENDS on those artists. The new system will only allow for basic shapes? Get real. We already have a 50kb limit which is outrageous for more complex SVG, but we deal with it. Effectively banning HTML isn't about performance. It's about censorship.
This is one excuse I can't believe based on how long lights perform. You want to increase performance? Fix the lights. You want to lose your game's aesthetic and appeal to artists? Implement this change.
Artwork is a visual form. Most artists aren't programmers so sending instructions with code to create works of art is absolutely unconscionable. Killing off artists isn't going to affect your bottom line, I understand that, but the removal of freedoms in expression or being limited should outrage any reasonable person.