I don't think so; but maybe I'm misunderstanding you. I imagine that very few people would have their trust depth set so deep that someone trusting their alts and trusting their alts and so on would make any difference. Keep in mind that there's a difference between positive/negative feedback and being on a trust list.
Furthermore, I suggest that if the trust system weren't so centralized, there would be less of a such thing as "enough trust to scam" in general. In order to have "enough trust to scam" user A, you'd have to actually b on user A's trust list (or th trust list of someone user A trusts, depending on A's depth). But getting onto any particular users' trust list wouldn't be very easy because there's no central "trust bank" that's going to make you look good in everyone's eyes (as there is now). Do you see this?
Hard to explain right now, here is a simpler version:
Member A does a few mini transactions with Member B and receives trust.
Member A continues to trade with others and receives more positive feedback.
While this is happening, Member A also leaves positive feedback to his alts, mixed in with legit feedback for trades done, making them appear more legit.
Member B and others start to trust not only Member A but also his trust ratings (not a good idea but it happens ALL the time around here).
Member B gets scammed by an alt of Member A, not knowing it was an alt of someone they have trusted. They made the mistake of trusting another member because someone they trusted left that member positive feedback several times. Member B also has left positive feedback for other legit members Member A has dealt with, making the feedback Member A left his alt appear normal and trustworthy.
Long term con. Just what can happen with the default list now. No different.
I've been buying and selling here for awhile now and know how some new and older members think. So think again before you say members don't trust others members because of positive feedback left. I know this for a FACT, as I get messages basically saying "I see you have trust from so and so, i can send first, send me your address?". I also get messages from others asking basically why they shouldn't trust members I have traded with and left positive feedback.
I'm a little tired so the above might not have come out right. You can see what I'm trying to say though. Something needs to change but what you suggested won't work IMO.