I haven't yet finished building my own.  But I've done mods on my electric, and have made some experiments.  I'll share a few thoughts here and maybe it will give you some thoughts.

The on-board preamp.. Yeah, they are often less than optimal.  Design or find a better one and you have a fairly easy upgrade.  I took the commercial one out of my electric in the first few months of owning it and replaced it with a simple FET preamp.  No regrets on that, I still feel it was a good move.

There is a good reason for keeping it onboard, though.  Noise.  The longer the cable run between the pickup and the preamp, the more noise that will be picked up and amplified along with the signal from the pickup.  So a small preamp very close to the pickup is sensible enough. 

However, I can think of no good reason to have the "tone" controls or volume controls on the instrument.  With some electric guitars, the controls are placed on the instrument in such a way that they can be adjusted while playing.  Not really workable with a violin, you can't curl a pinky finger on your bow hand around a knob and play violin.  LOL 

When I play electric, I mostly adjust "tone" settings on the amplifier itself, and set a max volume.  Then I use a volume pedal to be able to adjust volume while playing.  No need to have them on the violin, really. 

Other things one can leave off would be the headphone amplifier.  If one wants to practice with headphones, a small headphone amp can be worn on the belt or made to just be a small box that plugs into the 1/4 inch jack like one does with electric guitars.  The technology is already out there, and in many different amp "sounds" to choose from.

While we're at it, to save weight.. the batteries or power supply could actually be left off the violin itself as well.  Power doesn't take a battery on-board, it only takes a wire that could be the same cable as plug in to carry the audio, like with some condenser mics that are "phantom powered" from the mixing panel.

Now, if you don't mind a little weight from batteries on the actual instrument, wireless becomes an option.  I do that with my violin, and it is nice to not have a cable to drag around or stumble over.

Tuning.  Friction pegs are ok, and they are mechanically simple and relatively light.  They got invented before geared tuners.  Nothing wrong with geared tuners either, they just weigh a little more.  If you would normally use fine tuners, then geared tuners (whether something like uke tuners or geared pegs like the actually make for violins) instead of standard pegs and fine tuners on the tailpiece are def an option.  But my own current thought runs more to using zither pins, like a harp.  It takes a wrench to tune those, but they aren't prone to slipping or getting knocked out of tune by being bumped.  Fine tuning can be done with a standard tailpiece with fine tuners, and it would not be likely to have to take out the tuning wrench at a gig or session.  Or at most, use it once at the beginning and the fine tuners the rest of the time.

For fingerboard.. well, I like wood.  But acrylic can be cast.  Supplies for making molds and the resin and catalyst to use to cast the actual fingerboard can be gotten at most craft stores.  Not rocket science, people do it all the time to make paperweights and etc.  Heavy, though.  No weight advantage over ebony, and I would think it likely to get scratched up and less "pretty" fairly soon.  

The most complex part of the design process for me has been getting something that sits on the body like a violin does and balances similarly.  Sticking too much to "violin shaped" wastes the potential of going to a "solid body" electric version of the instrument and will make a pretty heavy violin.  So that is the part that has taken making mock-ups and seeing how thy handle and going back to the drawing board for me. 

Your mileage may vary.  LOL

But hopefully these are at least some fun ideas for you to consider and adopt, develop, or discard for your own design.  Some food for thought.