What's wrong with it becoming a service you pay for? This is, in-fact, what you get when you entrust someone else's Software As a Service with your data and workflows... You do not own it, they do and it is their right to charge for it just as it would be your right to charge for some service you developed and maintained that people found useful. It is also your right to move your workflows elsewhere or to a desktop / laptop resident piece of software that's not owned by anyone!
Whining about a for-profit product no longer having a free-tier is odd to me. Either be fine paying for the service (nothing wrong with that) or pickup software that is free; I for instance personally use org-mode and Emacs heavily for all of my personal information management.
I also do not understand the sentiment that every product acquired will slowly begin to suck; that happens for some products sure but the converse is also the case.
To be fair to Atlassian, I used to hate Jira a lot but in recent years had to use it for work and it quickly grew on me; they are putting effort into improving their services / products, modernizing their software development processes and technologies, and delivering updates to their software on a regular basis.
If you're going to contribute here, please be more constructive or detailed. Why not talk about your ideas for a project that is free that anybody could install on their servers that does what Trello does if you do not like that they may begin charging for Trello?