Though wouldn't such a change regarding Dr T have been more...

Though wouldn't such a change regarding Dr T have been more appropriately described in the trading halt as a significant staffing change, not a board change? My understanding is that Dr T's roles as an ED and CSO are independent, so he could step away from the CSO role if he wanted to and yet still remain on the board (especially so given the size of his shareholding). The announcement could infer that he is stepping down from the board and continuing in the CSO role, but implying the opposite would mean the announcement is really obfuscating the truth, IMHO.

Also, if it was something involving DT, wouldn't they have ample time to succession plan behind the scenes and have an announcement ready to go without requiring a trading halt? Unless of course he just woke up this morning and decided he's tossing it in, or they think their own company is a leaky ship and they need to halt to stop the news getting out - neither of which I feel are likely. Note that the same argument applies to JC as well, unless the relationship between he and the company completely broke down or something. The only other rational explanation could be that it's something totally out of the blue, like a health issue or other personal crisis (heaven forbid).

It may be wishful thinking, but in this context then I think the next-most rational explanation for the trading halt is it is required to complete negotiations with a party that is outside of the company and/or to facilitate the orderly management of some kind of capital transaction happening coincidentally with the board change.