in the last months, we saw again and again how users still love their old style 18650 SMPL mods.
We are very lucky, that we have since 9/10/2019 the very similar SP 18650 mod SKU 9709146.
Thanks to FT, to offer this construction again.
When we improve the construction from 18650 to 21700, this would be the perfect step.
It should not be a problem and cheap for a CNC machine, to make everything a bit bigger (21 - 18 = 3mm)
And I imagine, this 21700 SMPL would sell very good.
I would buy 5.

Edit: and in SS the 21700 SMPL/SP would be in OD and length smaller and also lighter,
than the discontinued Vindicator SKU 9695216.
Vindicator: 91 L - 70 Bat. = 21mm for deck and switch.
SMPL 18650: 79 L - 65 Bat. = 14mm for deck and switch.
SMPL/SP 21700 would be: 70 Bat. + 14mm deck and switch = 84 mm (Vindicator 91mm)
OD SS SMPL/SP 21700 would be 21 Bat.+ 4 Tube = 25mm (Vindicator 26mm).
Result: a very powerful and still very small 84 x 25 mm beast,
estimated weight should be around 105g, Vindicator 135 - 140g, SP 18650 81g.