(Just as a preface, I only recently (yesterday) started with Toki Pona and still have some way to go, but I do have plenty of experience with signed languages. Also, I'm going to introduce some information about signed languages to those unfamiliar with them, specifically stressing ASL gloss as a clear example).
Coming from a background in ASL and some JSL/International Sign with added interest in the BANZSL area, I'm definitely interested in having a developed form of TPL (Toki Pona Luka -as I'll refer to it-/ TPSL, PU, whatever you'd like to call it).
Seeing the examples of it online, as copied from Sonja's description of it, though, makes it seem like it is more of a coded system than anything else. This may be because TPL is described by four (three, in my opinion) things: 1. hand shape 2. location on the body 3. palm orientation 4. whether one hand or both hands are used--- [(which kind of ties to all three things above and doesn't feel like a distinguished category as it can be covered by both handshape(s) and location perfectly)]
In natural signed languages, five things are observed: 1. Handshape(s) 2. Location 3. Palm orientation 4. Movement 5. Non Manual Markers [(NMM-- facial expressions, mouth morphemes, etc.)]
TPL lacks two of those- movement and NMM, and I think that's where it starts to really feel unnatural and like a coded language. That, and it seems that the grammar of Toki Pona is kept completely intact, while signed languages usually do not follow the grammar of spoken languages, (often omitting unnecessary words like A/The/An---) even if they neighbour each other. This would be more of a coded system or pidgin than anything (think Sign Supported English for BSL or Signing Exact English in comparison to ASL). Things like ,,e" to mark a direct object wouldn't be carried over into sign, as location, movement, and facial expression would convey the information needed. Something common in signed languages is the use of topicalisation.
In ASL, ,,I went to the store" can be glossed as STORE-t-/ I GO FINISH// (or even FINISH STORE I GO//, amongst a number of other possibilities.) STORE with the mark -t- shows that it's topicalised. This means that your eyebrows are raised to indicate the role of that sign in the sentence. This happens in Object->Subject->Verb structures, which are commonly seen amongst signed languages (ASL, JSL, BSL, etc.). FRUIT-t-/ WE EAT// ,,We eat fruit." Time also often comes before topic and comment to indicate tense. YESTERDAY-t-/ YOU SHOPPING YOU-q-// ,,Were you shopping yesterday?" -q- here indicates a YES/NO question type and uses the same facial expression as -t-, often with a slight tilt to the head. TEST-t-/ YOU THINK HARD (body shift) EASY/ WHICH-whq-// ,,Did you think the test was hard or easy?" This uses -whq- expression (eyebrows furrowed, with mouth often forming the WH (who, what, when...) shape to ask a question that can be answered with more than a YES/NO.
TPL would likely follow suit in this grammatical pattern if a group of Deaf interacted and signed it.
So... Something like-
,,Mi moli" would likely stay MI MOLI//
A sentence like ,,mi moli e jan" would likely become: JAN-e-/ MI MOLI (MI)// -e- indicating the same thing as -t-, showing that JAN is being acted upon. Pronoun repitition is also common, hence why you might add an extra MI in there to indicate that it was, in fact, MI doing it.
TPL would also almost certainly make use of directional verbs. ,,Sina pana e pona tawa mi" would likely be one sign that moves toward the signer (showing- MI) whereas ,,mi pana e pona tawa sina" would be the same, just moving toward the other person.
Another way it feels unnatural... No use of any sort of classifiers! Sure you can get away with saying something is big, but signs are VISUAL, so it's better to show than to tell! Something like ,,ilosuno" (tool light) could convey the idea of a flashlight but also a lamp or any sort of fixture like it. In sign, however, one could show how the tool is held, and how light plays into it (grabbing the wrist and extending fingers to show rays of light coming from the end= flashlight) This still can perfectly tie back to ilosuno, but it isn't chained to the word-for-word base and quickly elaborates on necessary information without all the work around. Signed languages get to the point as quickly as possible when describing something.
While I think it was a nice attempt at initially getting something started, and allowing the Deaf community more access to conlanging, it leaves a lot to be desired, but definitely opens a gateway into developing something better.
This is definitely something that I would be interested in seeing develope, though, and I would love to record how users of it would interact and how it would compare to the complicated simplicity of Toki Pona. Hell, I'd even love to work on it with other people, too.