Vlars

Publisher is already at 1.7. What is the likelihood we will reach 2.0 within a year or so? I don't want to put out $40 for Publisher just to then have to pay another $40-60 to upgrade in a year-ish once we reach 2.0. 
Also, any idea if existing users will get a substantial discount once the upgrade hits? If we don't that'd be a bit of a slap in the face, having to pay as much as new users.

It depends on the level of the user, a graphic designer who studies design and produces work in exchange for money will appreciate the software, and we all know how much of a bargain to have affinity software for $50 and even down to $35 and $40 discounts. Other users might see them just as a nice game to produce cool images or make a document here and there won't value them as much as we do.
While open source software fail to provide professional quality features (having used Inkscape/Gimp and tried Scribus), they still have a value of providing accessible source code for programmers to learn how such software is made and how it works, providing free easy install alternatives, and many libraries/utilities can be even used by commercial software, even Affinity software incorporate a lot of them. Just check 3rd party licenses under Help/About...

Indeed. It's in fact a bargain, even if you're poor. Some people seem to have forgotten the real price of software and just don't understand the crazy amount of time, effort and passion developers, ui-designers, testers, consultants and what not put on software to create it so you can work faster and make more money with these tools.
Great professional software could easily cost hundreds to thousands of euros in a shop. And it used to be like that too for a long time. It has years of experience put inside it making you work so much faster you earn the money back in no time on the job. But some people in the age of 'open source', free apps (actually making money by using or selling your data) and dollar-apps for your iPhone or Android device, seem to have forgotten the real cost and value production software and compare real value software with buggy, but free, open source tools.
I think it's amazing Affinity makes this stable, performant and highly productive and professional software for only 50 euros and I'm very surprised if people are really this picky about this price to be honoust. To me that's a lack of understanding what it takes to create it and what makes it stand out above the 'just not right'-software out there.

Affinity publisher is aimed for professionals who create documents for print, not hobbyists. If you can't make $40 back from your work, it might not be for you in the first place.

You will never be forced to upgrade.  Version 1.x will continue to work even when version 2 is released.  You can choose to upgrade or not depending on if you want any of the new features that will be in version 2
 

The beta tester price is 35$.
 
I guess the first published version will be 1.8 
The 1.x versions were the beta, it would look nice to have the launch version start as 2.0

Are you seriously thinking about spending or not spending $40 for a pro level dtp software because you THINk there MIGHT be a paid update next year or not?
Either you like Publisher and want to spend the money, or you want to wait until it has a specific feature that you are currently missing and wait until then.
Don't overthink what could be and that you could be disappointed about something that might or might not happen next year and could or not could cost you 40 bucks that you don't need to spend if you don't need or want the new features or not that might or might not get programmed ... this kind of doubt and overthinking just makes you unhappy.

It is not a slap in the face. You are getting a product at a price that is vastly cheaper then the competition. I see the version number more as a number for the suite then for the individual product. If a bigger update (like a version 2.0) is in the works I am sure it would also take longer to make so I can't see it being released soon anyways.

They may not be “for life”, but the free updates tend to be for years.  Go for it.
I have had my Affinity Photo and Designer since January 6, 2017 with no update charge yet.
I believe that Adobe  InDesign is US$20.99/mo.