My version… a contemporary remake instead of a reboot!
Where do I begin? Oh dear, oh dear…
If I was to create brand new ThunderCats, I wouldn’t experiment with renovations and radically new directions. The original recipe worked flawlessly once and there was never a second attempt for us to learn from its mistakes. Given the huge gap without any new ThunderCats show for almost 30 years, I would definitely focus on a remake rather than a reboot.
The main issue with a franchise that has been left in limbo for so many years is the risk of acceptance by both the parents (who are previous, nostalgic viewers) and their children. And that’s what’s keeping an old idea rolling all about: guaranteed audience in favor of nostalgia.
Parents who are nostalgic about a franchise, would be enthusiastic about having their children watch a revamped show and play with its toyline just like they did in their age. It’s a natural thing. Children also enjoy endorsement from their parents, as they tend (or learn) to agree with their views.
No matter how great something is, what matters is the first (not literally) impression. I would rather call it the “surface impression”. What is surface impression? The impression a franchise (children’s show in this case) gives from its aesthetics (mainly), its toyline, its merchandise and a quick view of a trailer or segments of an episode.
I wouldn’t want to analyze what went wrong with the 2011 ThunderCats once again but it relates to the topic, so I will sum it up: parents received a very “foreign object” impression against their stereotype of the original ThunderCats, making them negative about it. In addition to a mediocre toyline, without parental endorsement, the youth wasn’t quite interested in something as bogus as “cat humanoids fighting a muscular mummy”.
The aforementioned idea is nothing without the whole recipe of the classic series. It sounds quite random and generic for someone who does not acknowledge the ThunderCats. Without the original “magic” that was the whole package, the basic idea stands weak outside the hardcore fan circles. Just like myself who, strangely enough, I’m a fan of the 2011 series.
So, back to the topic, what I would have done if I was head of department, director, creator, responsible anyway? I would remake the original series from scratch but it would be completely true to its classic counterpart.
Basically, the ThunderCats cosmos would be the same. Planet Thundera being destroyed, the elite of the thunderian race survives along with the Eye and their young lord, Lion-O. They land on planet Earth (then called Third Earth, maybe 5000 AD) and they face Mumm-Ra, blah blah. As for the characters, their clothing and their design, I would leave as-was. So what would make the show interesting and not quite a reheated meal? EVERYTHING!
First of all, while keeping the exact same looks, the characters would follow a contemporary, cutting edge design. Sleek, hi-def animation should make the series pleasing for all generations of viewers. Some may criticize the aesthetics of the original show as outdated but that’s very wrong. Superman, Spider-Man and pretty much every superhero, although going through changes, the eventually followed design is the unchanged original with contemporary design lines.
As for the story, it would completely expand the original. Instead of making up a brand new universe, I would explain every single aspect. Every character will have a backstory, there would be much less confusion. Mumm-Ra should be shown to have a first-Earth Egyptian background, how he ended up being how he is (probably asleep from 4000 BC till ~2500 AD when he ruined the planet), how he knew about the Eye of Thundera… and what the Eye actually is! Not to mention that the Kittens are adults, just a smaller, mischievous race of Thunderians.
The possibilities of expanding (and cleaning up the inconsistencies, 80s silliness :liono and mistakes) are endless in the case of the ThunderCats. What would also be a big bonus with such a remake is the possibility of a continuation to the ThunderCats saga, after Mumm-Ra was defeated in the final episode of the original series. This could be redone at some point of the remake and fans of the original would one day have a proper sequel to the original series! Additionally they would easily watch any episode with virtually no need for an induction.
Last but not least, actually essentially, I would do my best to acquire the rights to Bernard Hoffer’s original score or even hire him for re-arrangements. A really big proportion of the original series’ success happened to have come from the highly atmospheric and emotional soundtrack.
There was a background theme for numerous characters and situations, with a beautiful mix of classical, rock and ambient music. In a modern series, having those cues performed by a classical orchestra would completely wake-up the ThunderCat in adults and mesmerize their children 
I would like to end my post with a conclusive and wishful image:
https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-ash4/426132_336201903146574_1862788520_n.jpg