The problem lies with the demographics for PE. It is a young constituency with a relatively high incidence of highly educated graduate couples. While those that support Opposition will vote for LL in a straight fight, they will be drawn to a strong SDP candidate with better credentials.
I highly doubt statistics will bear out your conjecture in a significant way unless you are talking about Sentosa where every house or apartment costs several millions or tens of millions dollars. Someone who lives in an HDB flat, a private condo or a landed house in PE is not likely to be very different from one another as far as age and education is concerned.
Except for small number of elites and a slightly larger number of the deprived poor, the rest are in the broad middle class facing the same bread and butter issues. And it is this bread and butter problem that this huge middle class is concerned about - the high cost of housing, bus and train fares, COE and medical costs. Definitely very few will be interested in gay rights, whether they support it or not, or agree with what these NGOs are preaching which the SDP seems ever ready to champion.
Among those which are being publicly discussed, AYG and PT will be extremely attractive to voters in PE. If SDP fields them, I expect PAP to win and a photo finish between SDP and WP for 2nd and 3rd place. This will be a victory for SDP as it will establish them as being on par with WP. VW, while good, will suffer greatly in a 3CF. If he is the SDP candidate, then WP will maul SDP and there is even the chance SDP will lose deposit. If things somehow gets patched up and TJS becomes the surprise SDP candidate, I expect SDP to convincingly beat WP even if WP fields GG.
Except for AYG which is a known character and VW which you dismissed as not winnable, we are left with PT, who is unknown to most voters until a few days ago and even that only known to cyberspace warriors and just a list bearing his credentials. AYG had worked at the grassroots before but under the PAP. Don't expect the PAP swing voters to root for him especially under the SDP banner. They will probably consider him a turncoat and place their support behind the WP. So I don't think there is any positive thing going for these candidates.
As for TJS, evidently you are a TJS fan. In the first place, I don't think TJS will get into the fray if there is no guarantee of a win. In fact there is guarantee of a loss except in the case of a straight fight, unlikely with SDP contesting. If he goes in not to win, then it must be to improve SDP's standing. But what for? And be branded with yet another example of being an opportunist? I think he believes he is meant for better things - to be President, to lead his own party, not to be the second or third man in the party. Others yes but not him.
Now, assuming he got conned into accepting such a role. Can he win or do better than WP? Win is not possible whether for SDP or WP in a 3CF.
Can he do better than WP? The 24/25 % support he got in PE 2011 came mainly from the opposition supporters, a number of which, including well known names in this forum, admitted of making a mistake after TT got elected. The PAP swing voters actually put their votes with TCB (estimated 24%). About 10% percent of moderate opposition voters also go to him. This 10%, who would rather choose an ex-PAP candidate instead of TJS, will not go to TJS in a BE in PE. They are for WP to take. As for the 24 % that went to TJS in the PE, I am of the opinion that at least 10% of this will go WP's way (TJS was the only candidate clearly carrying the opposition flag) based on branding advantage together with TKL's 5%.
In other words, TJS is likely to get around 15 % from the real hardcore opposition and WP around 26% and Desmond keeping his 4.5% which I don't think he will in a 4CF. Let's split that 2% each to TJS and WP leaving 0.5% for Desmond. I am sorry to Desmond but let's face the fact. He is out of his element here. So PAP -54.5%, DL -0.5%, TJS -17% and WP -28%.
This conclusion is deduced from past results and performance without taking into account the possibility of swing votes in the past 2 years. I think with the MRT issue, the rise in COE, not much change in housing cost, although stabilized and the Palmer factor (which is worth a negative 2%), there is the possibility of a 6% swing vote. Let's share this out equally between TJS and WP and the results should look like:
PAP - 48.5% (YAM to return PAP's candidate as the MP for PE)
WP - 31%
SDP - 20% (TJS to return to no party status to prepare for the next election, be it BE, GE, or PE. His career path will be fixed this way)
DL - 0.5% (deposit forfeited and subsequently expelled from his party)
The interesting thing to note is that in the absence of both TJS and DL, WP would have won a narrow margin over the PAP and this forum would then once again debate on what had gone wrong in the election and a few high profile forummers would come out and admit they had made some terrible mistakes.
I am of the opinion that whether TJS is fielded by the SDP or not, the above results will remain. Party branding and what it represents will be foremost in the mind of most voters.