A keyword-questions tool - Culls question-based suggestions from various sources, including Google of course. User enters keyword, tool spits out a nice list of popular questions relating to keyword. A Niche-Research tool - Could show analysis of trend data of searches, perhaps based upon search suggestions, Amazon product popularity/trends, among other things. A more advanced version could be available only to paid subscribers. Maybe you already have some new tools in the works!
Would certainly be a nice tool to have... but it's an incredibly difficult task. Trend data means you would need historical data for each... and the only way to get historical data is if you were already monitoring the individual phrase for a long time *before* someone wanted to see the data for it. That's where the problem comes... it's impossible to know what keywords users are going to want to get data for. So the only other option would be to somehow try to monitor every possible search phrase (which is mathematically impossible).