I was playing around with it a little today and really all it needs is the various bits of math to be done for us. I get the reasoning behind not having it in there, and as a non-programmer who has done some "copy and paste" scripts to use APIs in Roll20, I can see the complication even small bits of random put in them, but (you knew it was coming
) I have also seen other sheets that have various options on the "Game Settings" page where you can choose specific rules to use.
For example, I have been putting together a Pulp-Era Isle of Dread campaign (punch Nazis!, ride dinosaurs!, delve ancient and non-human ruins!) and have decided on using the Pulp Cthulhu rules (dabbled with d6, but went another direction). When I chose them, the page had options for my to choose from, including the era and if I was wanting to use the Pulp Cthulhu rules. So, I chose what I wanted and the character sheet uses those rules. I guess what I am saying is that you could put it together where the individual user would be able to choose what rules they wanted when they put the campaign together.
I also get that you are not doing this for money (at least not directly, and the indirect route is long and winding), but I and quite a few others would absolutely love to have better RM options on Roll20. And, as it is a very popular gaming site, making the character creation and advancement process for RM as easy as possible would be the best way to get more players on board. That is one of the biggest gripes I hear about the game: takes so long to make a character that can die in 5-seconds.
Now, ICE, let me talk to you about importing the combat tables so they can be a built in feature...