I've had a stock Folgertech FT5 R1 for about a year now and have hundreds of hours of good successful prints with it. Many have modified theirs and that's part of the fun of printing, modifying and improving the machine. Of course many mods have perceived improvements of print quality, many are just wish-list, and some are actual worthwhile improvements.
The only thing that has bugged me about the physical part of the machine is the single linear rail on the X axis, the rail that supports the extruder. Linear bearings are very good in limiting "play" in many directions, but due to the nature of the bearings there is inherent play in a "rocking" moment - in the case of the FT5, this translates into play fore and aft at the nozzle end.
My answer to solve this and remove all unsupported movement is to add an additional linear bearing and rail assembly under the existing gantry extrusion. The rail is readily available from Amazon in a 350mm length and the cost is low. Link to Rail
The attached files and pictures show how I accomplished this. Essentially an elongated version of the melamine FT5 carriage, with some improvements in rigidity and print cooling. Of course we lose 15mm or so in Z capability, a small price.
If you only have one printer you'll have to print this first of course. The assembly procedure is to leave the existing rail in place, mount the new carriage to the top, then tighten, shim, adjust the bottom rail bearing until free movement is achieved. Patience will be rewarded with rock solid, smooth moving carriage that will be free of play and increased resolution tightness layer by layer.
The carriage is available on Thingiverse - Link to Carriage