I’m wondering this as with my project I’ve started to depend upon legacy animation, as I couldn’t figure out how the animator worked (seemed too complex for what I was doing). The current legacy animator allowed me to very quickly create a state machine to play different animations.
Now I’m worried because I feel like future versions of Unity (maybe Unity 6 or something) will lose the legacy animator for the newer one.
Several comments have said - they won’t replace legacy until all functionality can be recreated in mecanim, so until that day comes - legacy will still be alive. I’d like to see all legacy functionality to be recreated in editor without any code requirement - that would be best - although I understand a lot of developers still like to manage animation content via code.
fyi - there is no Unity 6.
Well…I was thinking in the future as far as Unity 6 is concerned…
Still hoping they don’t just up and leave it, as it’s just easier to have like an animation.play method (or whatever it is, haven’t used it in a couple of months). I’m just looking at all this code for this template and wondering if I should be giving an extra effort to use the new animator when the legacy animator just seems easier to use when coding.
I agree with every thing u said. As a programmer mecaninum is just a unessary step. Saying that I am using it for 2 reasons. Root motion which I only use on complex movement. Second one is retargiting animations. As I am not a artist this helps me out.
I really don’t understand why mecaninum exists. You still need to tell the animator how to animate in code. They should add on to legacy animations and add root motion and animation retargiting. I’m like u, I got my own state machine system for my platformer.
mecanim really doesn’t exist for you as a programmer - other than the reasons you stated - supporting root motion and retargeting, simple animation mirroring and animation layering which I’m guessing would be a bear to work out in code.
However mecanim is a great help for less code proficient developers who (like me) want to be responsible for setting up characters and the controllers - who find the code part totally frustrating and a road block to progress.
I advocate for keeping and improving the legacy ‘code’ system for people like you - maybe you’d consider advocating for keeping mecanim around and improving it for people like me - who aren’t coders. 
Well, I’m starting to eat my own words to a degree. At a local game group I just sat in on a talk about the animator.
Recently I made a script in where pixel character sets from rpg maker are importable into Unity and automatically sliced up using GetPixels() SetPixels() and the color[ ] array that you retrieve using those two methods. Basically I would slice up the images which would be 6x4 into two 3x4 arrays holding the characters walk and run frames. In this way you could just drag and drop a charset into your charset folder and it would do the rest for you, then you select what charset you want for your character.
The problem becomes limited animation (now you’ve just got walk and run with nothing else)…
Anyway, I think I’m finally understanding the newer animator is really for no coding at all and you just slice up infinite amounts of frames for your sprite sheets/character sets, create your animation files and drag them in, so that does seem pretty intuitive, but then it does have certain flaws like that it doesn’t support enumerators as conditions for an animation, which means that you have to assign integers for your animations and remember what they are (create a list of integers or something?).
Aside from me just rambling on for a while, the newer animator seems most useful for 3d character models for sure. It just seemed very complex to me coming into it. I was just too lazy to take the tutorials and sit there bored for a while absorbing the information when I just wanted a quick simple solution like legacy animation.