Past performance is not indictave of future results.
SP farming is an easy, and surprisingly robust way to get free money. If you aren’t farming every alt you can right now, you are doing it wrong. But given that, there is no reason it should stay profitable forever, and has been unprofitable at times in the past.
I’d say though if you need an army of alts for industry or ganking then it is a smart play. Even if the market returns such that SP farming is slightly unprofitable, having 12 or 24 low-SP omega accounts you can use is a major advantage on its own.
But I would say that you will spend a fair amount of time juggling accounts, logging in and out, buying PLEX and MCTs, extracting SP and selling them, setting up skill plans and the like that it isn’t totally without effort, although I guess a lot of that is front-loaded and once running, it probably only takes 10 minutes per account to make close to a Billion ISK - pretty good ISK/h. But there is also the opportunity cost of tying all that capital up into implants and SP.
A lot of Eve is like that though and if you are having fun planning and making spreadsheets and watching your SP farm grow, then have at it. I would just say though that I think we are in for a bit of a downswing in injector pricing right now with the summer activity drop and a likely appearance of a group of SP farms that were started in March with the first MCT price sale by CCP. You can see the tidal wave coming:
The number of SP injectors offered for sale has doubled in the last weeks, and prices have turned sharply down. I think margins on SP farms are going to be squeezed over the next months, so you might not be able to grow your SP farm as fast as your projections with the current numbers indicate.