From a response by Auctiva in a similar thread in the Everything Else section of the forums:
"We have no reason to believe that our templates (or any 3rd parties templates for that matter) will cause issues with the new search engine. We have not been told by eBay that they would, and the fact that our listings are still being found at the top of best match search results attests to that.
Hugh Williams, VP of Experience, Search, and Platforms at eBay, has given many interviews and webinar presentations about Cassini. He was asked specifically if the HTML in templates would hurt a listing's visibility in search, and he said that the search engine strips out HTML and only looks at the actual content in the description. "
Sounds like having a template will not disrupt Cassini's searches, and I myself have not seen any dip in traffic or sales while using Auctiva templates. As for mobile, I noticed that templates and embedded images don't really matter, as looking at listing through the eBay app on my Android phone those sections don't display unless I click on the tab to see the description. As long as I select the checkbox for eBay Optional Images when creating my listings, I will always see my images load at the top of the listing on my phone. If there is a slowness, it's likely caused by a network issue and not because of a template in the listing since that is not immediately seen.
I've also read on Ecommercebytes that eBay is also using better search result placement as a "carrot" to using their managed returns. Here is that story here: http://www.ecommercebytes.com/cab/abn/y13/m07/i17/s02
Sounds like eBay is becoming more like Google, you have to sign up for our different programs in order to get good search result placement, basically what Google started doing, pay to get good search result indexing. Pretty shady move on eBay's part.