Simple Fluid Tanks is not really needed in the pack due to the various other fluid storage options, like AE fluid storage, GTCE Quantum Tanks, and SoG Drums, and it has been stated that they are not performance friendly and have been known to dupe fluids occasionally.

With these issues and other viable fluid storage options, I feel like SFT should be removed. This will be similar to the MM removal, where it will be marked as deprecated for 1 release before getting removed.

In addition, if people want similar looking fluid storage, the GTCE tanks were reintroduced in #505, although their recipes may need some adjusting.

Complete removal of the mod is mandatory.

Simple Fluid Tanks is completely missing from CurseForge, to the point that uploading a modpack referencing it will fail.

I agree with your synopsis and the staggered removal approach would fit here, like what we're doing with Modular Machinery.

Removing the recipes for crafting SFT's components is easy enough, but I don't know that there's a direct corollary for SFT parts for conversion recipes. Perhaps like with MM's hatches it's best to just return the most valuable ingredient item in a crafting recipe.

If there is a similar sized GTCE tank, we could look at making a crafting recipe into the tank, but other than that, I believe giving the most valuable ingredient would work

It's a bit hard to map them onto GT tanks because while SFT tanks are a single type of block you just place as many of as you want, GT tanks have variable maximum structure size and storage density based on what material the blocks are made from.

It's a shame, I really like how SFTs look visually, I even made an entire room filled with them to store some fluids I had in small amounts earlygame.

I thought similarly and used them in my first playthrough back in 2019, but I have not opted to use them since. They have known issues as described above; there are alternatives available that may not look as cool, but are more reliable.

They won't be gone immediately as we always stagger breaking changes like that across two releases so players can update to the next version safely without losing anything.