[edit: a famous bit of company-is-a-feature carnage for reference: STAC vs. Microsoft: http://en.wikipedia.org/wiki/Stac_Electronics ]
Which makes me wonder why Matt can't get this championed internally or for someone's 20% project?
Startups need to solve difficult problems or they are nothing more than marketing firms trying to create a hype around hot air. Filtering email intelligently, including automatic anonymization of sensitive parts within the email, can be a difficult problem to solve, and I think there are many types of email integration that a startup could tackle based on the approach Matt suggests.
It doesn't seem like it's terribly impacted the other players, at least that's my perception. (could be wrong - someone with hard stats pls correct me)
My point being: that fear alone while is a rational one, should not be the only criteria to definitively say that an idea should not be pursued b/c it guarantees that you will fail in your startup
The danger is that when your app can be absorbed into something more popular. They don't compete with you — they just destroy the market for what you do.