Future Proof Your SEO
Google’s number one goal is to serve the best possible search result, both in terms of content and performance. Designing websites that are fast on all devices makes the internet better for everybody.
As Google continues to think about multiple search indexes, they have to consider why a result would be better in one method and not another. The merge puts more work on Google but provides a better result for consumers.
In SEO, optimizing for one search type also benefits the others. A smart SEO will look at what their current visitor percentages are by device, so as to assess whether or not it would serve business goals to optimize for the other (in the hopes on increased traffic), or to continue playing to their current strengths.
If you want to future-proof your SEO across all search types, start focusing on your content.
All of the content and design should serve a purpose. Consider how fast is fast "enough" and find your balance between content/design and speed. If making it faster doesn't help your business goals, then reconsider why you're focused on this particular effort.