Andrew Davidson suggested this variant, and L. Scott Johnson suggested some modifications.
All players start the game with no cards in hand (ie, a zero card hand size).
At the start of the first turn where you have a vampire in play,
draw up a hand equal to the capacity of the largest vampire you control.
This will be your hand size until your next untap phase.
During the untap phase of each turn, your hand size changes to match the
capacity of the largest vampire your control, even if that vampire is in torpor.
Elder Library, Dreams of the Sphinx, and Visit from the Capuchin function as normal.
Vampires with hand size increasing text function as normal.
Aura Reading doesn't reset your hand size to nine, it only increases your hand size
by two for the duration of that combat.
Some more options to try, suggested by L. Scott Johnson.
For those who don't like the "random" swings in hand size, we were also
thinking about a modification to the discard phase sort of rule:
Starting hand size is 4 (to match the crypt). During your Discard Phase,
if your base (unmodified by Elder Library, etc.) hand size is greater
than your largest vampire's capacity, your hand size is reduced by 1
(and you discard a card which you do not replace - you don't get your
first free discard during your discard phase). If it's greater, your hand
size increase by 1 and you draw a card (and don't get the first free
discard). If it's equal, you take your discard phase as normal (one free
discard).