Just wanted to see different opinions.
Plus, everyone has got to have an ideal subunit other than TTS. I just want to see if people will think that ideal subunit would be successful as TTS.

It depends on who exactly would be in that kind of subunit. If it would be a trio of popular members, I think it'll be successful (e.g. Jessica, Yoona, Sooyoung - although diffrent members are more popular in Korea, diffrent in Europe etc.).
Or if they make a trio: singer, two very good dancers and combine their abilities it could be successful too (e.g. singer: Jessica, dancers: Hyoyeon/Yuri/Sooyoung).

^agree with her

Agree with @miauu. Also if they have a really good song

Depends if it is a subunit of popular members and a lot of ppl want that subunit, like Jessica yoona and Yuri , ( which I don't want ) then they will be very popular. I want soohyoyul I also many other ppl wanting it but more ppl want yoonyulsica I don't think SM will do these subunits cuz they want to balance the singing and dancing , kinda like yoonsunsica sunny and Jessica can dance well when they put effort into it, while yoona's vocal are very good when she puts effort into it.

I t depends, the members left aren't that popular in Korea, just Jessica and Yoona, and lower, Yuri. But if they decided making an English album or Japanese either. Jessica, Sooyoung and Sunny could pull it of.

just give them SooSicSun or SHY, and you'll see...

No, there are high chances that they'll be successful, but I just don't think they can override TTS's success or even be as successful as them. There are many artists nowadays and I'm not sure if people will be paying attention to SNSD as much as before since they're getting older. And just like DaniMF said, there aren't other members that popular left beside Yoona & Jessica. TTS was a huge success, they got all charts kill and won 12 trophies in music shows, it would be very difficult to reach their level.

I don't think they'll be as successful as TTS because TTS already has some of the more popular members. There aren't other more popular members left other than Yoona and Jessica. However, I think SooSicSun would be popular but not quite enough to catch up to TTS. Another sub-unit I think would be popular would be if SM creates a duo sub-unit instead of 3 members. They could have a dance sub-unit with Hyoyeon and Yuri. I think a sub-unit with Hyoyeon and Yuri will be pretty successful.

After thinking about it, the only sub-unit that could make an album is SooSicSun. Nor Hyoyeon, Yoona or Yuri can handle 1/3 of lines in a song. Even I dude Sooyoung or Sunny can.