I suspect that at some time a government will limit the amount in TFSAs. I have INVESTED (not traded) my TFSA aggressively from the start and it is now over $220 K. Almost all my holdings never get sold. I have a friend at $260k. It could easily reach very large numbers, and for a couple it could easily reach over a million or much more as they get into retirement. I can't see any left-wing government abiding individuals earning say 75k a year tax free.
I made a quick and dirty spreadsheet where you save $5,000 2009 dollars per year, and earn 3% real returns (after inflation) . Those numbers are designed to be 2009 dollars, when TFSAs started. So the 3% is a 3% REAL return. In this case it grows to $839,000 in 60 years. So the nominal number would be far higher.
Might be tough politically to stop it, but it will be interesting to see how it pans out.
There are several big advantages to TFSAs as far as I am concerned.
1) You don't lose your contribution room OR YOUR ACCUMULATED VALUE if you decide to withdraw funds. With RRSPs you do lose it forever. Read the rules about intra-year withdrawals though.
2) If you die with no spouse with a HUGE RRSP the government takes half, because you are yanked up the tax brackets because it is all considered income in the year of death. That doesn't happen with TFSAs. Their withdrawal does not influence your tax rate.
3) TFSAs are tax-rate immune. It doesn't matter what tax rates are when you withdraw/make gains. Of course, with RRSPs this CAN be to your benefit if your tax rate is lower then when you contributed, but that leads to point 4...
4) RRSP refunds are not refunds, they are PAYMENTS for a STAKE in your RRSP. A refund is what the government pays you to become a partner. Don't be fooled by the illusion that you 'have' what is in your RRSP. You don't, you have that amount pre-tax. If you do not reinvest the refund completely, you really have sort of effectively made a withdrawal of that amount.
5) TFSAs do not require income to generate contribution room.