I don't support your suggestion. Good users are good users, and their qualities don't depend on their ranks. The forum has some genius guys, whom hidden behind the mud, and some day they might appear as shooting stars, like
nulliusThe forum, itself, has some staffs who hired when they stood at lower rank, like
Halab, whom likely hired to work as forum staff from Full Member rank. I don't know that there are staffs started below Full Member rank or not, but maybe.
DT members mostly been chosen from reputable users, it means they mostly are reputable, high rank users.
Another point is DT members will be chosen partially based on their past contributions to the forum, that in turn lead to most of them are higher rank users.
Lastly, fake voted DT members (at lower ranks, or even higher ranks) will be excluded from time to time, like this one:
User got voted into DT1 by sockpuppets
To conclude, I think that you suggestion is unneccessary, and the requirements that DT2 members should be higher rank members should be considered as un-official requirement, like what we have had so far with forum rules:
Unofficial list of (official) Bitcointalk.org rules, guidelines, FAQ