I've been thinking the TD system over, and I have two alternatives to offer.
1. Mage class characters can select a HLA ability called True Dweomers, which gives the player an innate ability "True Dweomer". When this ability is activated, they are offered a further list of abilities to cast. There would be several basic TDs in this pool. Once players had learned TD, they would be able to choose from a new group of HLAs on level up, and learn several other spells which would be added to the TD innate ability. TD would be able to be learned up to 4 times.
Additionally, the specialist mages would be offered several TDs they could learn (maybe give them an additional base choice as well) that cannot be learned by other specialists and normal wizards.
While this system could be very nice, it may be extremely nasty to code.
2. Have an ability called True Dweomer as above, but all of the spells under this tab are available after the first choice. As above, specialist mages would have some different spells in thier version of True Dweomer. This ability would be learnable 4 times (so can use it 4 times per day).
I'd be happy to see the first option, but if that one is too difficult and everyone wants some form of a true dweomer system, then I'd be ok with the second choice.
Do the planetars and devas still get Blade Barrier?
"In PnP, a pit fiend used to be able to gate in more pit fiends."
this is not true. he can gate demons who are less powerful then himself.
Actually a pit fiend can gate in two lesser baatezu or one greater baatezu (a pit fiend is a greater baatezu) per round with 100% chance of success.