The M8 was Cherry's first switch to use their now famed gold-point contacts. Just as with MX switches, Cherry also had an official line of keycaps to go with these. Below are a few of these.
A selection of official Cherry M8 keycaps.
From left to right: Two-shot molded ABS (from G80-0203), ABS with clear window for LED and engraved font, ABS blank, ABS with LED hole, engraved
Detail of G80-0203 1x1 sized key, similar molding artifacts to modern MX keycaps from Cherry.
Detail of LED keycaps
Detail of LED keycaps back. Note how the stem is trimmed at the bottom to provide enough space for LEDs in the open-housing design variant of the M8 switch.
Detail of a 2x2 sized M8 series keycap. Note how the stabilizer stems are trimmed on the sides to allow the keycap to bottom out on the low-profile M8 switches with a closed square housing.
A more modern variant of the default Cherry Corp spherical keycap. This has a higher profile than M8 keycaps and was already designed with the MX switch in mind.
Comparison of all Cherry keycap profiles.
Trivia
While the M8 spherical keycaps are compatible with modern Cherry MX switches, the stem on a MX swiitch is much too long, which can cause the keycap to wobble quite a bit while typing. To bypass this, Cherry produced a special design MX switch with a "M8 adapter" as a stem, which prevents the keycap from sliding wobbling. Photocredit special MX key: Brother Dragon/yab8433408 from the KBC forums.
Cherry still produced the M8 keycaps upon request until 2010. Individual blank keycaps as the ones pictured above could be ordered with no MOQ, while double-shot-molded keycaps were available with a MOQ of 300 pieces. Production for both was stopped at the same time as the Cherry MX double-shot production.
The end. As always, feel free to use any pictures in reposts/translations on KBC, KBDMania, Geekhack or OTD.
And yes, the no-led part would be fixable only through a teensy or other custom controller (afaik 
