As it stands, I'm still evaluating Nifty and I think everyone has gone over the pros enough so I won't do that, but I like a lot about it. I've been using Clickup which is almost perfect for my uses and as it stands is much better for complex projects. But I think Nifty can get there from what, as a developer, I think are very achievable updates. Some things from Clickup I'm definitely missing:

FIRST-CLASS SUBTASKS
I don't see any reason subtasks can't have full task capabilities while providing the option to show a simplified view for users that want the "checklist style" subtasks like the current setup. There could be an option or menu to activate the detailed subtask view for advanced users that need full capabilities for subtasks e.g. to assign custom fields and attach media to subtasks (we do this regularly). This is something we absolutely need and I think would be a dealbreaker over time - the major PM solutions do it this way for a good reason. Nifty said they originally had those capabilities and removed them for simplicity, but simplicity of a layout can be addressed by design, settings and options.

PROJECT FOLDERS and LISTS
See how Clickup did this. Right now, a project gets cluttered really quickly without the ability to add folders within that project to organize groups of tasks. It's almost unusable for a large project. Clickup even goes a step further and allows you to create lists INSIDE of a folder or OUTSIDE of the folder depending on your needs for organization. This functionality is really needed.

GROUPED VIEWS
Clickup allows you to see a list of "everything" in a project. For example, if you click on a project, you'll see all tasks for that folder. If you click on a folder within that project, you'll see that tasks for that folder. You can do this all the way up to the workspace. Makes it really easy to get an overview of all tasks and get an idea of how the project is going in terms of tasks.

TASK SUMMARY
In Clickup the list of tasks and Kanban view show some color-coded icons depicting how many substasks that task has and how many are complete. Really easy to get information about the project at a glance. Super nice feature!

KANBAN VIEW
Minor UX quirk here - in dark mode, it's really jarring when a big default white scrollbar is beside every kanban category that's longer than the page height. Again, see how Clickup did this with a custom UX-matching scrollbar that appears on hover over tasks in that stage instead of a bunch of huge white scrollbars showing at once.