There are actually many champions who were conceptualized to be much different that the software was capable of achieving at the time of their implementation. As Riot continues to gain greater technology and resources, they are able to re-tune those champions to be closer to their original intention.
There is also the fact that other changes to the game have indirect impacts to the game that effects the ability for an outdated champion to feasibly remain relevant. There is likely to come a point where it is better to overhaul a champion to bring them up to a point where they are relevant with the current balance of the game, and will more readily able to advance along with the projected direction that the game is headed.
And lastly, one of the main appeal-points that this game has to draw it's audience is that it changes fairly often. The way that information is made available to the community actually generates a lot of hype around changes, even from a controversial perspective. Ultimately, this is a very effective business practice. Notice how much more Warwick has been played, even since the rework was officially announced, compared to just before.
I don't know if this will ease your concerns at all, but I genuinely believe that Riot is very aware of what people enjoy about each individual champion. I would not be surprised if Singed is on their radar. However, Singed is probably one of the more unique champions that I can think of. He is played very differently than most, if not all other champions, and I would be very surprised if Riot didn't honor at least a part of that unique play-style.
. Later on maybe 
who knows.
Next class to rework are tanks Vanguards and Singed is not one, so for now he's safe