There are Webway Gates projecting buff-aura, there are Waagh Towers providing timed buff on cooldown. So, it might be something new to let Tyranid one to level a constant de-buff
As far as I know from DoW2, Tyranids are supposed to be the Zerg-like Hive (yeah-yeah, ok, throw your rocks at me), deploying the largest quantities of troops as to be compared with other races.
So.. instead of giving them what other factions already have, how about some spawning grounds, producing low-tier units for free (limited in number that may be tied to the current Tier) and projecting some sort of synapse-aura, lifting default speed\performance de-buff (may have more properties with tier advancement\doctrines)?
You can't provide a graceful micro to the horde due to the number of units you have in control, so it seems logical to me to make an accent on their placement, instead (Orks, kind of, already have it, but it spiced up with Scrap and abilities it unlocks, as well as how their Elites consuming it).
Imagine, you can spawn 5 *Gants early with the battle-worth of 2 TM's squad. You would have a catastrophic casualities with each engagement, which have to be replaced somehow, but you would also have an ability to spread all-over the map, that would be better to limit until the later phases, when more diverse play take it's place and more types of units can be fielded (one of them may provide mobile synapse-aura, by the way).
Of course, other buildings can be allowed within the aura, enchancing production, extending the aura, like Capillary Towers and many others suitable for the "Hive", so the opponent entering your territory would have felt the difference.
Oh, and if all Tyranid Elites may provide that synapse aura by default (if it's not another backflip for WH40K fans), it may enchance Tyranid's ability to create dedicated battle groups around the map (though everyone would just blob it at the end of the day).
Also a part of your numerous force might be dedicated to some "economical" tasks like corpse-collecting.
This way DoW3 may incorporate one more elemtent from the top RTS'es of the past (I mean SupCom 1 by this).
And, by the way there is already a precedency in CoH2 on how british infantries\osttruppen buff handled, and it's, indeed, in lifting a constant de-buff.