Currently, bitcoin must be redeemed by providing input to a script which
results in the required output.  This causes the attached amount of bitcoin
to become available for use in the outputs of a transaction.  Is there any
work on creating a shorter "transaction" which, instead of creating a new
output, points to (creates a virtual copy of) an existing (unspent) output
with a larger amount attached to it?  This would invalidate the smaller,
earlier UTXO and replace it with the new one without requiring the earlier
one to be redeemed, and also without requiring the original script to be
duplicated.  It is a method for aggregating bitcoin to a UTXO which may
otherwise not be economically viable.

The idea is that there already exists a script that must be satisfied to
spend X1, and if the owner of X1 would like to have the same requirements
for spending X2, this would be a transaction that does that using fewer
data bytes.  Since the script already exists, the transaction can simply
point to it instead of duplicating it.

This would also enable the capacity of lightning channels to be increased
on the fly without closing the existing channel and re-opening a new one.
The LN layer would have to cope with the possibility that the "short
channel ID" could change.

Dave.