Your best option is if limitation don't change is not to have a group of 32 players together, because then you lock out potential adversaries for your blockade.
Not necessarily tbh. There are many issues to overcome in this regard indeed. But I am quite hopeful. The key thing to realize is that, unless technology and netcode improves leaps and bounds before eventual large fleet mechanics are implemented, some compromises will have to be taken in design.
Instancing is the main barrier for large fleet size encounters obviously. Star Citizen is in the same predicament, although their instancing rough size estimates so far seems to be slightly bigger than FD own estimates. Still, this is to be seen.
But, despite the instance limit, there may be creative ways to handle such big encounters.
One such way for example could be to develop a Command & Control structure for fleets that allows for "admirals" to pre-assign a preferred hierarchy and a structure of subteams within their fleets. Such that if, for example, a sub 32 fleet encounters another enemy fleet resulting in a total combined of more than 32 ships then the server would decide to split those fleets into several instanced encounters, each instance comporting a fraction of each fleet and whose composition would be based on the "admiral" pre-design hierarchy and structure. Ultimately the split would be decided by the server instancing algorithms of which that hierarchy would be but just one variable probably and thus tehre would always be an element of "unkown" in the actual decided split. I would not have a problem with that randomness if it comes to it... it could be easily rationalized as "fog of war"

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One could conceive also a degree of communication between instances so "admirals" can eventually decide to order or queue certain ships to transfer in between instances, as long as there is room enough in them (as some ships are destroyed or withdraw etc) when needed.
This kind of multi instanced encounter mechanic would also bring a fun layer for the eventual C&C aspect of the game whereby Admirals would need to really have a well thought out and balanced hierarchy and structure in preparation for such "splits".
But this is just one such idea to handle large fleets. There may be many many others. I wont doubt FD is capabale of creative thinking in order to handle these.