What they're dreaming of is: lots of big companies write their vital business apps on top of Meteor. They spend billions of dollars on middleware and application servers that helps them deploy, monitor, and control these apps across their 100 divisions and 5 data centers, similar to the billions of dollars they've spent in the past on Oracle, WebSphere, Tuxedo, Tibco, etc. Meteor does an IPO.
Failing that, they're hoping that we can replicate the success of JBoss ($420M to Red Hat), XenSource ($500M to Citrix), or SpringSource ($420M to VMware), all of which took open source software and sold it to the enterprise, and each of which did it under the direction of one of Meteor's new advisors (David Skok, Peter Levine, and Rod Johnson respectively.)
As for time frame, they are patient and expect it to take a long time. They know that it takes years for a platform to be adopted.
(edit) I am honestly surprised to see a VC invest into (what amounts to) a fundamental technology. Though, given the valuation bubble we are in, it makes sense. VCs now have a choice between continuing to speculate by funding upload widget startups ($2-3M a pop, two years of runway) and putting money into the core tech. Fingers crossed, this becomes a trend.
We have a 10+ year lockup on our money -- we can go to 13 years without too much effort, and longer if necessary -- so there's no near term pressure for financial return.
The goal is to build Meteor to its full potential both as a technology (including open source) and a company. If that happens, the long-run return will be fine.
Salesforce bought Heroku for a boatload of dollars. It's not difficult to imagine that someone might acquire a next-generation application development platform. Just one possible exit.
