The ideal (?) scenario would be if SIAF distributed a heavy portion (25% of it's shares) in one blow, and then the rest (up to 50% in total) over time.
However, SIAF can't do that now after saying that they will give out 50%. Especially not while TRW isn't listed yet, people would just loose faith in both SIAF and TRW (fraud, fraud, scam, scam, wolf, wolf etc).
They have also said that their lawyers say that it might be viewed as trying to manipulate the PPS. I wouldn't know, but that seems strange to me - then you could use the same argument for a regular cash dividend :-)
Also, SIAF might want to get it's ownership below 20% so that it becomes a true holding company. That way SIAF gets way more transparent; they will just book whatever the PPS for TRW etc are, and then we could go to TRWs reports to get to know TRW&co. The complicated corporate structure is one obstacle for people who wants to invest.
Now, if the rumours of CA possibly listing before TRW, then there might be no downside of giving all those TRW-shares in one go; If they decide to do things differently with the CA dividend shares, then the market knows that SIAF can (and will) do as they say.
Besides; as soon as TRW gets it financing, and/or CA gets a deal outside China, there will be no need for SIAF to distribute TRW-shares year after year - there will be plenty of cash to distribute :-)