TBH, I think the SDM failure issue has got blown out of all proportion.
I have no doubt that there have been some failures, but I suspect people who have had an expensive lens fail tend to be a lot more vociferous than the majority who have nothing but satisfaction with the DA*s, creating the impression that there is a major issue.
I have 4 SDMs and 1 HSM and have had no problems with them at all.
OTOH, Pentax would do no harm byextending the warranty on them.
It's a real shame that people are being put off them by rumours and gossip. They are missing out on some world class lenses.