RSA vs ECDSA: it's not the size of the executable but the size of the data.  I thought it would be impractical if the block chain, bitcoin addresses, disk space and bandwidth requirements were all an order of magnitude bigger.  Also, even if using RSA for messages, it would still make sense to do all the bitcoin network with ECDSA and use RSA in parallel for only the message part.  In that case, everything that's been implemented up to now would be implemented exactly as it has been.