Annual is unappealing to most subscribers - but some percentage will go for it if it's available. Like 10%ish (may vary but definitely a minority). This minority will smooth your cash flow quite a bit.

What evidence/reason do you have for the claim that annual is unappealing to most? (I'm not advocating anything here, I'm hoping to learn something.) I would assume the same thing if there is no discount (no compensation for extra risk and time cost of money), but I can only guess at how people respond to annual options with various discounts. Do you have anything more (including your own guesses)?

One data point, for TeamPassword[1] we offer monthly and annual as described and about 1/3rd choose the annual plan. Would love to learn more data points to see how our mix is versus others.

[1] https://www.teampassword.com

Putting a high sticker price in front of someone is another one of those speed bumps to conversion. As the proprietor you'd probably prefer them to go for $70/yr, but $70 is a big difference as an impulse or low-deliberation purchase from $7. I'm the annual-plan-buying type, but I'm atypical in a bunch of ways - e.g., I live in a high cost-of-living area so while I'm not actually a money-disregarding rich person, my impulse-buy range goes a lot higher. (annual = 10x monthly is very commonplace)

Has anyone ever tried:

Annual plan only available after 6 months of membership?

While I understand that sounds counterintuitive, if not odd, it:

a) offers an incentive to stay.

b) with that goal line in mind, the offer of annual when getting there has special meaning. As opposed to a random "you've stayed. You must be happy. Wanna go annual?"

Again. I hear what you're saying, but in a nudge-y / Hooked sorta way it might work.

Bloomberg (magazine not terminal) did that for me, annual plan wasn't available during sign up (though there was a cheap 3 month trial); after a few months on the full monthly plan, offered me annual plan at a discount.

I took it.