Better strategy to avoid multiple unnecessary reindexes on upgrade required

My client is rapidly approaching the stage when an upgrade from say 4.2 to 4.4.3 cannot be done between EOD Friday US and SOD Sunday APAC, mostly due to the amount of time spent indexing.

From what I can tell the upgrade above requires 6 full reindexes.

Sure, some upgrade tasks may require the updated indexes but often not, eg UpgradeTask_Build660 directly follows 646, both of which do nothing but a full reindex. Surely some optimisation can be done here? Perhaps the indexing could be postponed until a further upgrade task says that it requires uptodate indexes, or the last upgrade task completes.