Currently, it is impossible to tell whether a spindle is idle or transmitting power. There should be a visual and possibly auditory cue.
To render a block as rotating, a block entity is required. I would prefer to cut down on the number of block entities for performance reasons. Is this unfounded? Additionally, rotation would have to be synchronized between spindles.
Sparkles (probably black or wood-coloured) are a good alternative that theoretically should not require block entities.
Auditory cues could get loud and obnoxious.
Judging from the above, particles seem to be the best way forward.
Currently, it is impossible to tell whether a spindle is idle or transmitting power. There should be a visual and possibly auditory cue.
Judging from the above, particles seem to be the best way forward.