My two ducats on tech groups and their implementation:
(1) Firstly, despite their names, techgroups should not be assigned according to religion. This may seem obvious but it is important to realize that techgroup is not decided by religious tolerance.
For example: Spain was religiously intolerant -- classicaly so. Nevertheless, Spain had a magnificant army and a thundering economy during her heyday. Even after losing her superpower status, the Iberian giant remained a major European kingdom. All this despite her idealogical extremism.
Another example: Poland was religiously tolerant -- Catholic but tolerant. A great army with valiant leaders but a steadily deteriorating government/economy and no naval power to speak of. Paradox choose to model this trend by giving them a techgroup drop in the second century of the game (the merits/drawbacks of which I don't want to discuss here).
I could site more examples but I'd rather get to the point.
(2) The criteria for assigning techgroups should be two-fold:
-- Distance from the center of Europe. Where this is in Abe is up to debate.
-- Approximating political or economic handicaps too difficult to represent in any other way.
The first criteria is the more important one, in terms of game balance. Nations near the center of Europe have stronger neighbors and less options for expansion.
Here's what I think about the tech groups of muslim nations in Abe:
Granada:
I'm strongly against dropping her to orthodox techgroup at the start -- and not just because I don't want to see my baby get gimped. Although her neighbors are not strong at first, Granada is in a position to be attacked in force later and is isolated from her natural allies. More importantly, Granada will need a comprehensive research strategy to succeed in MP. One thing orthodox nations cannot usually do is research naval tech, something that is advisable for Granada.
Granada could probably survive with orthodox tech, but I don't want to see them lose Latin tech on the basis of religious intolerance -- particularly given the fact that I didn't develop their events with intolerance as the norm. From the outset I've envisioned Granada as an bona-fide aristocratic Renaissance Kingdom with a strong muslim flavor. The Sultans of Al-Andalus are more likely to be motivated by political, feudal and romantic reasons than religious ones.
The Caliphate:
On the other hand... I do believe that the Caliphate should remain in the muslim techgroup. MP strategy for the Caliphate should be very simple. Defence is a minimal concern, unless an agressive and cooperative pair of players are manning the KoJ and Byzantine Empire. Research strategy is relaxed -- Land and Infra are the only things that are necessary. Expansion opportunities are abundant -- Arabic and (later) Persian culture provide wonderous opportunities for this country sitting on the crossroads of two landmasses. My opinion is -- muslim techgroup is a necessary brake on their power.
The Golden Horde:
There is room for debate here, certainly. They have ornery neighbors... but also have some nice strategic depth, especially at the start. Some punative events but nice cultures. Some good opportunities for expansion, but a lot of neighbors looking to pummel them. If the GH were to be given orthodox techgroup (and I'm not saying they should), it would have to be by event later in the game -- 120 to 150 years in, at least.
Personally, and for reasons I'll not examine here (unless someone wants to discuss it), I'd lean more towards leaving them in the muslim techgroup. They'll be a good challenge in MP and SP that way.
North Africa (sans the Mameluks):
Sure. They should probably be in the orthodox techgroup. I've always kind of felt that they got the big shaft in vanilla EU2. Morocco and Algiers at least should have some teeth. I don't really care about Tunis and Tripoli too much, they're likely to be fodder for Sicily and Egypt anyhow. Judging from the events already written, I'd say I'm not the only one who feels this way.
The Mameluks:
I don't really think the Mamelukes should get orthodox tech from the start of the game. Maybe by event, 8-10 decades in, but not at the start. The Mams were a highly traditional warrior caste with a heavy political stake in maintaining a medieval status-quo. The Mamelukes were the example I was following when I decided that a Malwas takeover of Granada would lose Al-Andalus their latin techgroup.
Of course, I don't think any nation should be rail-roaded into any set path in Abe. And I don't want to get on Kaigon's pecks -- the Mamelukes are his baby, not mine. Though not as strong as the Caliphate, the Mameluks share some of their neighbor's advantages -- a relatively defensible position, at least two unopposed vectors of expanion (although the Horn of Africa sucks monkey pole). A strong, renaissance Egypt would be a cool thing to see, but I think that there should be a delay on that for gameplay reasons.
**
Ehhh... oh well. Enough talking from me. Just don't mangle Granada without telling me, ok?

Cheers.