Hi rtwdave,
That should certainly be possible – but might require a little customization work.
The basic approach I might take in this sort of scenario is to set an action to “listen” for ical requests (and you might also want to listen for some other flag, such as an “unlimited” URL parameter, so as not to interfere with ordinary month view ical exports), then modify the query parameters to extend the date range – so, some knowledge of working with WP_Query objects would definitely be required as a minimum.
Of course, if your site has a truly huge number of events you may still wish to set an absolute limit on the number of results to be returned in order to avoid memory issues.
I hope that gives you some ideas to investigate 🙂