I just took out the 50gb @ R199 x24 month contract in-store. No problem adding it to my existing pre-paid number.
But the store employees were adamant that DataShare now only works to Contract-recipients, regardless if it was Personal or Business contracts. I didn't believe them , as recently updated terms only mentions this limitation for Enterprise/Business contracts + no uproar in this forum, so I took the chance and took out the contract.
They also told me all the data (50GB) would be sharable.
The verdict is in:
(1) only 30GB of the 50GB is sharable. the MTN app shows 20GB is listed as promotional data and can't be shared.

At least I took this out on my main number rather than a new spare SIM, so I should be able to use a good chunk of the promotional data.
(2) there is no problem setting up the Datashare to Pre-Paid numbers, i've already done it and it's working.
Plan details:
Plan name: Mobile Internet Platinum
Plan expiration: 26 Oct 2027
Rates: Voice R2.15/min SMS R 0.35
Note: rather high voice rates.
I think I have a few days to cancel under CPA, not fully decided yet...