I think you can be FI if your stache won't cover your current lifestyle, IF you have made a well-thought-out decision to have a larger lifestyle because you don't mind/want to continue working, but are perfectly willing to scale back on that lifestyle should you choose not to, or be unable to, continue working.
That is the situation we are in right now. Neither of us feels like our career is over, though I'm closer to feeling that way than DH is. I consider us FI with a NW north of 1.7 million (includes retirement accounts, other investments, land, college savings, home equity), but we like raising our kids in our big old house in a nice, safe neighborhood in the city with good schools, and we like international travel (took the kids to South Africa a few years ago, Europe is on the docket for next summer, China the year after). After a number of years of a higher savings rate, we have chosen to scale back our savings. We max out our 401(k)s and put 1k/month into college savings, but other than that, we are spending the surplus on travel and home repair/maintenance. Plus I took a pay cut to move to the non-profit world to do work I'm more passionate about and cut my hours to 80%.
At any point if our careers are no longer rewarding, or our kids need us more, or we just want a change, we can downsize, pay cash using the equity in our current house, and retire with a scaled-back, but still pretty darned nice lifestyle. Now, you could argue that we aren't FI, having not proven we can live on less, but when you remove daycare (not needed if not working), mortgage, international travel, and higher property taxes, insurance, utilities, and maintenance costs of this house, we are already there. So I feel pretty confident in saying we are FI.
I think even when we retire, downsize, etc., I can see us doing some consulting work or teaching the odd class both for fun and to fund things that are completely discretionary, but potentially outside the budget.