Of course it might not be a big impact, as many never gets into foiling.... But apart from that:
Those times where you bought a big 17 m2 LEI to ride in lower winds on a big TT are gone, history for most.
15-17 m2 "normal" LEI kites are utterly useless for hydrofoils as you implied in your post, way too heavy for the 5-7 knots where the "size" alone would be appropiate, and they can not fly.
So yes, the market for these are not the same now.
A trend has evolved the last years, typically aiming for 10 to 15 m2 superlight or light LEI kites (Storm Voyager, Zeeko Notus Air, Airush Ultra, North Mono etc etc), as these are perfect for hydrofoiling in sub 10 knots.
And they can also be used for light wind waveriding or freestyle, as they turn even faster when lighter and less struts - but on cost of upper windrange and behaviour of course.
Regarding foilkites it is different - as the really big race foilkites around 20 m2 are used by all racers, and the big racekites 10 to 15 m2 are used by freeriders as max size.
The older "huge" 19 and 21 m2 foilkites (Old Silverarrow and similar), that were easy to handle, are gone in hydrofoil terms, just like the 15-17 m2 normal LEI kites are gone here.
These foilkites are too heavy, and they often have too much grunt for hydrofoil - does not work well...
Instead, just like with the 10-15 m2 superlight LEI kites, there are coming a new trend now with "freeride" hydrofoil foil kites (OZONE Hyperlink t.ex), so 10-15 m2 foil kites that are light and a bit lower aspect and easier to handle than the utmost race foil kites, but not as heavy and slow and grunty as the older huge foilkites.
Whether it will be a small niche market, or not, time will tell, because many will buy a used racefoilkite at a reasonable price instead.
As the majority of freeride hydrofoilers (around here) dont like foilkites, and opt for light LEI kites instead, it makes sense there is a much bigger market now for the 10-15 m2 light LEI kites that are good for other board types than hydrofoils also.
But as people and the hydrofoil sport progress, some non racers might want a better performing kite in light and marginal winds, like the freeride hydrofoil kite, eventhough more expensive