As the game evolves, I believe that the Hydra (and Eldar Firestorm - that is if we get one in the new rumored Codex, and it has similar rules, which by all means I expect it to) is going to become a staple of some lists. Let me explain my thoughts.
With the Blood Angels supposedly getting their new transport, Melta becoming more prevalent and taking it on cheap choices like Land Speeders (which are fast skimmers), Dark Eldar rumored on the horizon (which will continue to be the kings of skimmer spam), and even the Imperial Guard getting Imperial Navy support in the form of the Valkyrie/Vendetta you can expect to see more fast skimmers on the table collecting cover saves like there's no tomorrow. Honestly, do you expect the flier-esque love to stop there? I don't.
The Hydra has the height, and the gun to deal with these comparatively low armor values and punch through the Cover save these vehicles get with its awesome Autocannons. It's cheap too - in fact, very cheap, comparative to a Warwalker in terms of an Eldar player standpoint, I would even wager it is more survivable than the Eldar walker at this point as well, and overall comparative to the offensive firepower it can dish out. Plus, you always have that Heavy Bolter for backup in desperate times. It can damage MEQ and monstrous creatures with nearly equal ease and safety from the supreme range. If you play Apocalypse, the Hydra is almost an necessary component of your Anti-Air support - that is if you find yourself on the receiving ends of bombing runs.
All of these reasons and more are why I'm building Hydras.