I think it's a smart way to reboot a series. To heal the wounds of the past *cough* 3d games *cough*, NRS gave us MK9 with updated versions of most of our fave characters with a new Kombatant (Skarlet) and an awesome guest character (Freddy) thrown in. This brings back the hardcore fans and reintroduces the series to a new generation of gamers that whether or not they are familiar with the series, missed out on the hype of yesteryear. Skip forward to today where the next stage of the reboot is happening with MKX. To further bring MK to the new generation, it's time to shed some of the classic elements that may seem outdated or even corny to the modern audience: 50 million ninjas, cyber ninjas, the palette swaps, etc. It may not be intentional but I see this as NRS making a game that this generation can call their own much the same as we did back in the day with MK1.
I for one am pissed that there's a pretty good chance that my main won't return. Much like it's time for me to step aside as a gamer for the next generation, it's time to say goodbye to some of what we know to make room for new favourites and new memories for this generation. It's not a bad thing, it's just growing pains that must be endured. I was involved with the Soul Caliber community when V was announced and released. The amount of hate at the new characters was unreal. Sigfreid is an old fart? Where is Taki? WTF is up with Patroklos and his sister? Sure the new Taki plays the same, but she doesn't illicit the same feels to a Taki main when looking at a different avatar while playing. It was bad. At least NRS is being smarter than Project Soul and doing more than transplanting a moveset onto a new character. Take Cassie for example. She has similarities to both Cage and Sonya but still looks like her own character (at least at this point anyway). I think NRS is doing an excellent job of bringing the "feels" that we had back in the day to a new generation with a gam they can call their own and not a 20+ yr old one passed down like a children's tale.
Actually, speaking of Cassie, I am less inclined to agree that her inclusion means the exclusion of Sonya and Cage. While from a technical standpoint she shares some moves with her predecessors, there is still much room for the originals to be their own characters. Also, with the story starting immediately after MK9, there is much to do and both Sonya and Cage will need to be a part of that; given that they are among the few surviving heroes of the "War with Outworld". Not to mention that they would be instrumental in "passing the torch" to the new generation of characters. So I think there is still a possibility for these two characters to be involved in MKX: without a doubt in Story mode, quite possibly as playable characters as well.
Imagining how cool his moves would look with the new engine. You could say the same for almost every other character as well though lol... But yeah, not worried at all. And it's not like it's only Sub and Scorp and the rest is new characters. There will be enough returning ones. 
