20-Year Prospect
It's not great.
Sure, distributing doodles is easier than ever due to the internet, but nearly all of the comics available online are free. So while this is likely going to be a side job for all of the foreseeable future, the earning potential is going to steadily decrease as print media loses popularity.
There are several ways to drum up a little cash online, but these are generally only viable for those who have extremely popular comics (source). You can make money off of ads on your site, or through donations, but one of the best ways is through selling printed anthologies of your work to your die-hard fans.
As time goes on, this field is more and likely to transition into being more of a hobby than anything else. Even well-established cartoonists tend to hold other jobs these days (source), and it's not going to get better anytime soon.