Currently I estimate that their are about 250 general choices for units in Warhammer Fantasy Battles. This is based on the 582 items in the webstore with about 15% bundles and bits and about half of those Heroes of various types who need some counting but not every single one distinct. The new Age of Sigmar is supposed to have about 40 warscrolls as part of the free download. If you divide those up against the 9 groups you get about 5 each which is probably broken down to like combat infantry type, shooting infantry type, cavalry type, warmachine/monster type, and Leader/Hero Type. Given that their were like 15 factions before the End of Times means that each classic army might only have a unit or two that really represents its nature. Interesting issue here is all those super expensive End of Times Show Piece models might be pretty hard to get through such a compaction. Maybe they will return as the "Gods of War"hammer in the future.
While it is hard to complain about free rules, I think existing players with large collections are not going to be very happy with the homogenization of their forces. Now the question is as GW moves forward and releases new units and books will more of these old models have correspondences or will they intentional design them such that they do not match past models well.
GW does seem to be going in the right direction in some senses with the free rules and making the game playable at lower entry points where something like a battalion box is a playable force as opposed to a joke. This sort of helps them with a expensiveness of the individual miniatures but does go counter to their injected plastic molding production which is about volume.
Maybe this is inspired genius since if you make the units generic enough and the games smaller, people who did not think they could field a WFB army now can make up a Age of Sigmar force out of what they have to give it a go. Instant player base maybe larger than just the active WFB players. While I did not think is possible that I could field a force for this game as I have no units just lots of fantasy skirmish, I do have 2 units of elves from Mantics Dwarf Kings Hold Green Menace and more than enough Elven Heros/ Fantasy Monster Types to Fill it out. Also got 2 units of Undead from the Dungeon Saga Kickstarter (originally for the first Dwarf Kings Hold) inbound for another small force. Ofcourse those models would look really funny verses the huge new AoS minis since they are all pretty small compared to old GW fantasy scale.
I am wrong. All sorts of units for all the old armies.