For added weapons could be the Dai-katana, maybe throwing projectiles, new spells, shouts (as they created dragonrend, why not others?), mounts, and homes.
The Blades didn't create Dragonrend, and I've seen nothing to indicate that they ever created any shouts at all. I'm not sure there's any record of
any non-dragon having created a shout from scratch, except for that one.
And to use any shouts at all, they would first have to be taught how to do it. Not taught
a shout, but taught how
to shout. The only people with any experience teaching this ability are the Greybeards, and they are NOT going to teach the Blades anything.
Even if there was a way to teach them all, it would take years for it to really amount to anything. Ulfric spent almost a decade studying with the greatest masters of the Thu'um available - and he was handpicked to be their student - but after all that time he only learned two shouts.