Eh I doubt it. Trial twinks would become a problem for the normal players in the bracket, and they don't want to piss off current payers for the sake of (possibly maybe not) future payers : /
I seriously wonder
how.
'Sunwell Twinks' in 70-74? Sure, I can see the potential for issues there, and to a lesser degree for 80's in 80-84 as well (due to the agrressive scaling that takes place in that bracket). The 'Rampart Twinks' raining on AV-weekend 'loomers parade can't happen anymore from what I understand, with every Vanilla account having been upgraded to TBC.
But without access to the things that make those kind of toons possible - Epic Gems from the next Expansion, end-game Enchantments/Kits etc., maxxed Professions and, in short, the AH - your average capped Starter account isn't going to pose any real problems for your average Heirloom toon in the BoA Battlegrounds, let alone for 'Heirloom twinks'.
Admitted, as I still prefer to play in Emberstorm/Glutsturm, and play mostly in the late evening my experiences may be a bit skewed, but in XP-On most toons I encounter are at least of the 'Enchanted Heirloom-and-rags' category, and in 15-19 already I've been the only one without 'looms quite a few times.
Sorry, but I find the idea that level 20 toons clad in some ilevel 21-ish Blues with +1/2 Enchantments would pose serious issues for 21-24 toons clad in (de-facto) some ilevel 30+ Blues with +15 Enchantments rather comical, and while of course you have the odd double-AGM 20 that can match a 23-24 'Heirloom twink', with the far larger player pool people won't have run-ins with them with any regularity, let alone more often than with the 'Heirloom twinks' they already encounter.
Or, to put it like I did elsewhere, it makes even less sense to put newcomers in the same queues as level 24 Twinks than it does to put them in the same Battlegrounds as Heirloomed toons.
But yeah, given that Blizzard puts the most attention to the part the people that pay for all this (end-game PvE'ers, not irate Twink players) prefer the most, I don't see any changes coming soon.