The only puzzle value that is added by this is that level creators could then enforce "a lemming can't blow up in the first 5 seconds after it spawns".
Perhaps it has value from an execution difficulty point of view, but as execution difficulty is specifically something NeoLemmix tries to reduce, not increase, such a suggestion has no place in NeoLemmix specifically. I'll make this very clear: NeoLemmix will never get timed bombers back; not as the standard behaviour, not as a player-side option, not as a developer-side option.
Lix follows a similar philosophy in this regard - perhaps even more tightly than NeoLemmix does (in particular, there's a big difference when it comes down to "fairly simple to implement cosmetic features that are nice to have but not critical"; Lix is likely to say "minimize complexity, cull / don't add it" whereas NeoLemmix is more likely to say "sure, why not") - and I doubt you'll see this there either.
For SuperLemmini, timed bombers could fit, but I also get the impression Tsyu isn't even remotely considering additional skills - so it would have to be on the basis of "it reverts to timed bombers", or perhaps "the content's creator can pick one or the other, but not mix them". (Of course, I might be wrong and Tsyu might be willing to do such a thing - you'd have to ask him.)