We have to remember that AV vendors adjust their products to maintain or improve the protection. The criminals try to improve their attack techniques to get profit. There is a kind of balance between these two sides.
In my opinion, it is probable that:
- New threats count will still increase as it could be seen for several years.
- Threat type and attack surface will increase too.
- Detection technologies and threat hunting will improve to keep balance in relation to points 1 and 2.
- The probability of infection will not change substantially in the next few years.
I mean the above in the context of home users. I am not sure how this will change in the business environment. But, I cannot see the signs that could suggest the big changes there, too. Anyway, I even did not try to calculate the infection chances in businesses. This would be probably a lost cause. 
