Small list of features for Attuned shards to make them a lot better:

1. Stacking of the same coded shards.

It is a bit iritating when you try to make multiple plates all teleport to the same other plate... and each occupies separate slot!
I made six shard all connected to same plate, yet they don't stack together.

2. Attuned Arrows

You can attune arrows inside of plates in order to mark them to set plate.
Shooting entity with arrow teleports it to the plate. Does not work on bosses in order to avoid destruction.
Recipe would require you to put arrows on side slots and single Warp Dust in the middle slot.

3. Modified Plates

Putting different items in side slots modifies properties of plate:
Lever let's you turn the plate on and off. Turned Off plates can't be accessed from other conected to it plates. To turn plate off, you have to charge it with redstone.
Redstone plate of any kind let's you detect any entity being on plate.
Wool will mute the sounds.
Glowstone Dust gives short glowing effect after teleporting into the plate. Could be a nice alarm system!
Glowstone Block would empower the light the plate produces, incase you try to avoid torches as much as you can.
Putting potions allow for one time effect on player after teleportation. Could be a nice trap! Or maybe you want to be immune to fire when going into Nether?

4. Cosmetics and waterlogging

This one is mostly begging for cosmetic options...
We have sandy waystones, where are sandy plates?
Or mossy?

Tho to be fair, I would like few more variants of not just plates, but also waystones, sharestones, portstones...

Also - being able to waterlog those blocks in any way would be really cool. Be it fully or partially.

5. Cheap re-attunning of Shards/Arrows

Putting Attuned shard or shards with single warp dust in any slot let's you re-attune stone to new plate.
Attuned Arrows accept the same price.

I hope you like some of the ideas.