There is absolutely no incentive NOT to use the reducing level adjustment variant rules if they are introduced. There is no effective XP COST associated with it, because the XP TO LEVEL is reduced by the exact same amount. Effectively, this completely removes the penalty for taking la races of +1 or +2(The only ones allowed here anyway) since they start gaining xp at the reduced ECL as soon as they get high enough level to remove the LA at no cost, and many characters reach ECL 10.
Also, I would have purchased templates for characters if that rule was in place, because as I said, there is no reason not to do so mechanically speaking. Here's a quick summary of how it works, LA +1 hits class level 3, ECL 4, (4-1 =3*1000=) 3000 xp spent. You need 6000 xp to reach ECL 4, you need 3000xp to reach level 3 normally, So you spend 3k xp to reduce the amount of xp needed to be level 3 by 3k, and reduce the xp needed for all future levels by 1000, so it's a net gain in the end.
LA is supposed to be a penalty, the buying it off rules are for powergamers. Casting the WISH spell a single time or dying in combat once costs you more XP than buying off a LA +1.
A Few other things to note:
Edit: got taken care of in the final revision