Disclaimer: What I will post here is the culmination of over a decade and a half of my work and experience. Please be kind.
Ok, with that out of the way, there are few things that must first be considered for the design direction, even at the conceptual level.
1 A mobile wearable should not be a watch.
I have seen so many smart-watches over the past few years and before them, so many watch phones going as far back as Samsung's SPH-WP10 in 1999. I have owned a few watch phones over those years as well and I can tell you both from professional and personal experience that a wearable that tries to be your watch will ultimately fail in the mass market.
There are so many issues with this approach, from the obvious style factor, to the impracticability of the tiny unusable screen that will no doubt grace its face.
Q: What happens when someone who wants to wear their favourite Chopard, Breguet or IWC buys a smartwatch-styled phone?
A: They will leave the smartwatch behind in favour of a traditional phone on the occasion that wearing two watches just would not work.
Remember, the wrist was not where that class of timepiece started. It started in the pocket and fashion and practicality dictated its final resting place on your forearm. So if we take a cue from history, we will see that copying the wrist watch isn't the way forward for wearables.
2 The wearable should not be the accessory of a larger device but should be the core of an ecosystem.
Your usage scenarios should dictate what kind of UX and UI you have at the time. Therefore, the wearable should be small, kept out of the way and worn for the convenience of transportation. The ideal interaction with it should be done with a series of wireless dumb accessories designed to take your input and give output in a form-factor that matches the application.
3 Do not put a screen on it.
Aside from the obvious style issue (ala point #1), there is the fact that in order to be usable, your screen will dictate the size of the wearable and to a certain extent, its battery life.
Use an alternative method of display technology for the scenarios where you will be interacting with it directly, sans wireless accessories.
4 It must be water-resistant.
A practical wearable should be something you put on your body and not think about as you go about your day. Having to worry about your wearable when it rains, when you sweat or if you go to the pool is counter-intuitive and unnecessary with today's technologies.
5 Battery life is everything and contactless wireless charging is a must.
Being able to charge your wearable without having to take it off will change the way people use it for the better. Contactless wireless charging that can put a few metres between you and the charger is the ideal solution and it exists today.
6 Processing power, storage and RAM are your make or break specs.
If you are going to build a wearable that is worth buying, it should be able to replace more than someone's aging iPad. Today we can make a dual 64-bit processor wearable with 16GB RAM and 512GB SSD, that runs Windows 10 and has the power to rival your Core i5. It won't be in the price range of your entry level Apple Watch or Asus ZenWatch but then, why should it be?
7 Understanding your target price point is important.
You wouldn't expect to buy a new Core i5 powered ultra thin tablet for the price of a cheap smartwatch. So then don't try to build a cutting edge wearable that can replace your tablet/laptop at the price point of the Apple Watch.
8 Security is paramount.
A wearable that is properly made will be more attractive than a traditional smartphone. This also means it's more likely to be stolen. If your files are not well protected, then this will be yet another potential threat to your privacy and identity. If the wearable uses biometric security to encrypt its filesystem and has as few physical interfaces as possible, then while it may be a pretty target for thieves, it will be nothing more than a pretty paperweight without its owner.
9 Design from the perspective of jewellery first, technology second.
While many of us engineers tend to overlook the aesthetics of our creations as a vital point to be examined at the start of development, we should always remember that what something looks like can already be more than 50% of the battle won when you are trying to get the final product sold.
Taking the above points into consideration, the wearable should look like a piece of jewellery. It should be elegant, yet subtle. It must be something that a 15 year old will want to wear and at the same time, something that her 60 year old grandfather would wear as well. You must make it a piece of fine jewellery that takes design cues from the established fashion houses.
Do not make a piece of technology then slap a fashion brand on it after the fact, like some famous product designers have done.
10 Support multiple Operating Systems.
A worthwhile wearable must not be limited to just one OS like most traditional smartphones. As with a laptop/tablet PC, this is a portable computer that will be used by a diverse range of end users. Much like the Eve V, it must be able to support all of the major Operating Systems that may be used by its target market.
With these 10 pints as a discussion starter, I will give you guys some time to mull over the design direction before I post Part 2.