I was asking the exact same question. I did a dummy booking for SYD-SIN-LHR in 2008 and was quoted over AUD 23,000 on the website, with only the SYD-SIN sectors in R.

At present the very top F fares for this route are around AUD 16,000 on all major carriers including QF, BA, CX, SQ. However if you are smart you can usually get the fare for around AUD 12,000.

It would appear that SQ are charging a 50% mark up on the current top F fares (23,000 vs 16,000) for the SYD-LHR route with only one sector in R. Based on this pricing, this fare would surely then double to around AUD 32,000 if both sectors were in R (once the A380 is on the SIN-LHR sector). This would be double the current F fare.

This represents an emormous increase, and far above what Emirates are charging for their Suites product.

My view is that SQ are seeing whether there is a market for such a high priced F/R product. It is an interesting experiment. If R is full, then they were right and there was a market for this product. If R is not full, well then they can always reduce the prices.