Will there be such a point or am I missing something?
[1] http://blog.backblaze.com/2011/07/20/petabytes-on-a-budget-v...
[2] 200MB more than the amount currently in my gmail; I have email going back six years and I never delete emails, but I'm not a heavy email user.
EDIT: Formatting
Sorry, physics humor. Real answer:
Drive space is very cheap today. It is not hard to offer several GB per user. Email as it is currently implemented only supports messages of about 10MB each at max, while typical messages are text-only or include only a few low-res images as attachments. For typical users, it is therefore not probable that they will ever accumulate data at a rate faster than is currently the case since it is a protocol limit. Historical trends have also shown that larger file transfers are simply routed to other methods, so it is unlikely that email will be overhauled simply to increase the per-message size limit.
Monetizing it as a free service in a way which is not onerous to users and convincing users that they should use your service versus a more well-known and established provider are the hard parts. Solve that, and you've got a good competitor. Don't solve that, and you've got a money sink.
I think Google really wants G+ to link all of the Google services we use together and bring people onto services they weren't previously using. For those which live in Google this is great but for those which only want to try G+ or use one service it puts more barriers in your way.
(Not that the particulars matter, but I find gmail slow, ham-handed in its organization, ugly, and strangely lacking, given its origins, in the searches it supports. Not to mention the fact that the cursor periodically disappears when composing messages on one of the three machines I use it on.)
I'd much rather pay a small sum of money to a provider in Europe ( = better privacy laws).
A few non-techy people have asked me if there are email services that don't read your email for contextual ads, and they would be willing to pay. So I think there's a market there, albeit a smaller one that the free email provider one.