[note: I have nothing to do whatsoever with Intercom, just my 2 cents]
Case in point, we sell our product for $99/year with a $20/month add-on. Some people got this for $39-$79 for life, and I'll never change that because I wouldn't have a product if not for their early support.
I'll also never ask our current customers to pay more, provided they stay active.
The overhead of keeping early adopters alive at initial prices is not significant, so there is very little risk in grandfathering them in. However, raising the price risks driving brand advocates (like those commenting here) away, or at best, making them disgruntled.
I guess I just don't see the upside.