*snip*
I'm just preparing deltarpm v3 which has support for combining
deltas.
The point is that a delta is always between two exact rpm versions.
If the client has left out some updates the server can combine the
missing deltas to a single one (combining is quite fast as it doesn't
need full rpms) and send it instead.
*snip*
Or the client download two deltas and combine them? Having the server do
processing won't be taken ligthly by mirrors...