Hello @mstrauss. I have an FT-5, and like you, was drawn to the "beefiness" of the structure. I am mildly interested in the CNC potential also. I already have a large CNC machine, though.
I believe you will find the 2020 sections are not the point where you will see deflection because of weight/ additional weight on the bridge supporting the X axis - it will likely be the tolerances in the bearing block, or the connection between the block and the bridge. These parts will likely deflect more. By the way, the 80/20 company has a deflection calculator on their site, so you can see the impact of STATIC loads on the sturucture. Keep in mind the FT-5 components might not be from 80/20....
Regarding laser. Any small laser will likely weight less than the NEMA extruder drive stepper, so no real worries there.
Regarding the CNC conversion.
First of all, I have not seen the kit...
Yes, you are correct, the dynamic loads on the structure and the drive components (belt tension, pulleys, take-ups, etc.) will most likely be the points of concern, but we won't know until it is out and several folks have had a chance to provide feedback to the community. This will likely take a month after introduction - at least.
Here is my personal input:
Would I buy an FT-5 again? Yes
Would I buy it if a CNC option was not available?:Yes
Will I modify the FT-5 printer: Already have (the FT-5 is a great place to start - smile)
Will I likely modify the FT-5 CNC offering: Yes, if I purchase it & I likely will modify it.
The other item I didn't see you list is your intended use/ expectations for the CNC capabilities. This is important:
* Materials (wood, plastic, aluminum)
* Cut feeds
Hope this helps.