I did some research just now. The OGL states that one must have the
Representation of Authority to Contribute: If You are contributing original material as Open Game Content, You represent that Your Contributions are Your original creation and/or You have sufficient rights to grant the rights conveyed by this License.
Which means to me that we should check to see what 4e-style things already exist in the SRD, and what does not (this is what OSRIC did), and completely gut what we do not desire, and use/modify/add what we do. After a few minutes, I discovered that a lot of 4e systems already exist in the
SRD, or could be reasonably modified from what is contained therein. This is what I found, and my thoughts on them.
Healing Surges - There already exists a mechanic called Reserve Points in the SRD. It could be easily extended to include "reserve surges." Sound familiar?
Defenses - This can be easily modified from what already exists, and the precedent to do so already exists in the "Players roll all dice" alternate rule. Smelt it with a spell-attack system (coming later) and what one might call versatile saving throws (where one uses the best of two score modifiers for saves/defenses) and we have the 4e defense system, sans the half-level and enhancement bonuses.
Rituals - These can be easily modified from the incantation system. Gut the annoying 3.5 style BS, make it easy to remember, overhaul what we want, maybe even reincorporate the "dangerous" buisness, and you have new-and-improved 4e style rituals.
Skills - They needed an overhaul anyway. We just define the ones we want how we want them. Easy.
Resting - This seems like an easy system to employ. It becomes an alternate rule to the "realistic" natural healing system. Since this needs an overhaul from 4e as well, we just include our new versions of short and extended rests (whatever we decide that means) and boom. Done.
Backgrounds - Such a system by that name already exists in the SRD, but I cannot make ups or downs of it at a glance. I suggest implementing a system that would be equivelent to the 4e backgrounds called "Character Origin," which would give a +2 bonus to a skill, make something a class skill, or they could learn a bonus language. Boom.
Skill Training - Star Wars Saga Edition does this. Since we are in favor of a math overhaul, this could probably be used, but I do not see it in the SRD.
Attack Spells - Since the "Players roll all the dice" buisness shows how spells can be used in attacks, we got this down.
4e-style spells/powers - This would be moderately to highly challenging overhaul, but it is possible. It would require a lot of fat cutting, and maybe also some creative compromising. Many classes might look more like they do in Essentials (which I do not consider a bad thing). Once such a system is implemented, cross-class compatibility should be easy.
Themes - The most problematic thing I can see here is its name. Like Weapons of Legacy had to be recoined Legendary Weapons, themes will have to undergo a similar titular adjustment. Other than that though, it seems like an easy rule to implement: "themes" or whatever simply add new features, RP hooks, and a compliment of alternate class features/powers/spells.
Magic Items - I don't know what we are going to do about this. Ficus that shitsu. It can come last as far as I am concerned.
Conditions and Other Rules - Since we can gut and readjust the rules how we want, from what I can tell, we could just record how we deviate from the RAW SRD suggestions, and publish those "new" things when we get there. The liberty to gut spell save DC's, skill points, ECL etc is a great comfort to me.
Encounters - Since we want to do an overhaul of this, I say we figure that out when the time comes.
My point being that I think we have most of the 4e rules already covered, or easily reinvented under the OGL. Is there any other major system of 4e that I have not covered here that we need to consider?
If not, it is my vote that we follow the path to OGL, modify the system math tremendously as we deem fit, and after that fill in the system with delicious fluff and create a beautiful system.