If the guy is just - for want of a better word - genetically shy and a sole-contributor type who likes to take tasks and bunker down and churn out code, implementing any of these suggestions will probably make them snap quit.

I think the better question to ask here is, can you get the input you're looking for out of the guy through a method that best suits their style. These suggestions are very 'force the round peg into the square hole' - like; the guy's shy? ok, we'll fix that by ramming him into situations where shyness isn't permissible until he gets over himself.

It may be better to figure out how they can best deliver their contributions; some people prefer to digest input and write emails than engage in a 'face to face' because they see that as inherently adversarial and tend to back down.

At the end of the day, not everyone is going to be able to stand up and advocate loudly for themselves in a group scenario; that does not make them a bad contributor. You need to evaluate their ability and ensure that your processes do not mean that an insistence on 'face to face, talk it out, say what you mean' style of communication in the business results in their contributions getting steamrollered.