SPP-SDA lost everything in GE 2011.
The only consolation prize for SPP is a NCMP seat. Nevertheless Potong Pasir is a very good single seat that even its lost still secured a NCMP seat
The opposition parties that will play a role in 2016 will be WP (needless to say), NSP, SDP and a new TJS force. The rest, including SPP, RP, SDA, won't count for much.
If there is no TJS force, then likely the TJS grouping will hinge on NSP.
This one in 2016, the centre of attention will be on WP, hence likely will affect the chances of other opposition parties, based on less publicity, less attention received etc.
WP might nab another GRC. Unlikely to be 2 or 3 more. But all opposition representatives will be from WP after 2016.
Having 2-3 GRCs will be when WP's real problems and challenges of unity will start, so 2016 to 2021 or to 2026 may be a trying time. By the time, they will also have a change of figurehead as LTK would be old - meaning more potential issues.
If WP fails on too many counts, PAP is likely to redominate, at least for a period of time, rather than a new opposition party arise immediately.
NSP is unlikely to win a seat because, as always the "borrowed platform", will spread itself too thinly as usual, with or without the TJS force. However a large amount of candidates expected.
SDP will still continue to stay where it is. Too little can be done in the short time, overcrowded scene and their tendency to stay small from high turnover. But still significant numbers, and increase from 2011.
Potong Pasir will be gone, which means SPP will go Bishan-TP, likely not make it, then go into oblivion by 2021.
RP is mostly likely to contest a GRC only or 2-3 single which will be entrapped in 3 corner fights, get damaged and say bye in 2021.
Likely, SDA may not contest in 2016 at all.
Overall, the result will hinge on how the PAP performs. If any non-WP opposition can nab a GRC, means WP will win enough to become ruling party and the whole story would be different.