Well, as far as i can see you are proposing to prune everything but unspent outputs. That's nothing new. The only thing that's new is doing this by transfering everything to a developer and then back to individual wallets, so in your scenario the developer holding that super account can fck up everything if he wants to.
Doesn't sound very good to me.
What is the alternative according to you ? Prune the blockchain by individual clients/users ? How can such individual pruning be trusted ?
Even for pruning it must probably be done by a trusted source, for example the bitcoin source/software but there has to be a way to verify that it was done correctly. Thus the main developers could be the source of the trust. It must however also be veriefiable that it was done correctly.
The client can be build/coded in such a way that it checks if it was done correctly, otherwise it would not accept the new blockchain.
There could also be other benefits: Perhaps new bitcoins could be introduced, I am not sure if that makes any sense logically ? I think it could.
If I remember correctly the ammount of bitcoins is based on the number of blocks in the block chain.
By reducing/rebuilding the block chain this could give new incencitives to miners to keep participating in bitcoin mining.
However perhaps there is an unforseen problem with this idea... suddenly there would be more bitcoins then the rules allow... so this will have to be looked further into if this is a problem or not.
If it is a problem, the super account could also introduce a new root for the block chain discribing what happened, how many bitcoins were mined and start from that offset to keep everything as it was.
Building this new block chain could be done offline to take it slowly. Alternatively it could also be done in a distributed fashion, but might require new algorithms. The new block chain transactions awards miners as usual... though these rewards go online/accessible when the new block chain is in effect.