There are a few things holding me back from this fully replacing Bashed Patching and these are basically just features that WB has, which I have become accustomed to.
One is the WB system automatically gathers up all the leveled lists and provides this to the user for management. This is an excellent feature and one of the main reasons I use Bashed Patches. Smash could provide the same functionality as an option for the user. If they are just making a single Smashed Patched for their mod list (as I assume most users would do), it would be nice to have the option of including merged leveled lists into the Smashed Patched just as WB does; without having to worry about anything extra.
The second feature holding me back is the ability to include game tweaks right into my Bashed Patch. This reduces plugin count and/or unnecessary console commands. It's a time saving feature. I've also always desired this feature to be expanded upon so that all the game settings could be included. This way users wouldn't have to worry about setting them up elsewhere. A few checkboxes and you're done.
Lastly, from what I can tell and from first impressions, Smash currently requires knowledge of the Bash Tag system to get its full functionality. This is a fading...dying?...system which few are fluent with anymore. Finding well written documentation for the tags, by itself, can be an en-devour. Then learning how to apply appropriate tags to mods is another. I think this is evident in that we have become accustomed to WB auto-selecting the mods it wants to merge and most users just going with it. Smash doesn't have this functionality, from what I can tell.
It could be possible to do an initial scan of the mods to collect some of this information and provide a couple of presets to merge a few basic plugins with basic edits, as WB does. Then provide the option to merge leveled lists from all mods and include game tweaks. If Smash could get to that point and do a better job at patching than WB, then WB would fall out of use for its patching function due to Smash meeting its goal of Smashing being better than Bashing.
These are just my observations during my short time with the program.