Googlers in general won't tell you about upcoming features because we have a general policy not to discuss them publicly. But, trust me, each Googlers would love to let you know what is coming up and what he is working on!
There are many reasons as to why lots of [big] companies have this policy, just to list a few: keeping a competitive advantage, avoiding any backlash if not delivering the promised feature for any reasons - reasons could be: lack of ressources, shift in priority, legal, privacy, patented, deal with third party falls off, staff quitting... This policy is usually taken quite seriously and a person's job would be on the line (+eventual lawsuits for loss of business) if he unveiled an upcoming product or feature without having this cleared beforehand.
Now there are many cases, product or features where this doesn't really apply nor makes sense and there are no risks of not delivering and no loss of competitive advantage. It might even be beneficial to talk about unreleased feature in some case. However, in many companies it's not usually possible to trust every single one of their employees to have the overview that would allow them to mesure if that's the case. Therefore, since there is too much at stake, it's usually safer to simply have a general policy not to discuss upcoming feature and to be secretive. Also as companies gain in scope it is usually harder and harder to gauge if secrecy is necessary and would usually need approval from a large number of people (PR, Legal, PM...). So, as external interest/demand for information grows for popular companies, it is not always worth the effort to ask permission to discus each particular cases.
Also about Deadlines, in the case of companies such as Google, it's not generally good to give any as they are usually very hard to measure because of the many code dependencies and things that can come-up internally, (for instance illness of the few staff working on the feature) but also because that allows to keep an agile way of working and avoid loosing time "measuring" in advance how much time things are going to take. So since there is no real obligation to give a deadline, it's usually preferable not to give one as a precaution to avoid any disappointment (and associated backlash) when not meeting them for whatever reasons.
Now given all this, it's a good sign that we announced publicly that we are working on a Linux client, and that typically means that we are committed to it and that we are already working on it. (Otherwise we would have sticked with a canned response such as "we appreciate your feedback... we are always working on improving Google Drive ... The linux community is very important to us etc..." or at least the wording would have been different). That basically meant we cared enough to cleared this up with with a lot of people and take the "risk" to pre-announce something.
As for public repository, currently the Google Drive sync clients, unlike our API Client libraries, are not open source. But "This is something we are taking into consideration as we are always looking to improve Google Drive" ;) More seriously there can be many reasons why companies are not open-sourcing things, first there are some overhead in doing so (maintaining the external repo, external project, patches, writing nice code) and also we wouldn't be able to use 'hidden' yet-unreleased APIs (not saying it's the case here).
I hope this clears things up as to why we behave like we behave, and I think this applies to most [big] companies in general and totally understandable given the over-competitive, legalistic, patented ;) climate surrounding the tech industry now.
PS: Sorry this was a little long :) And sorry for not telling you more about the Drive sync client for Linux, but as you now probably understand: I can't (but I will ask the team if we can tell more) :)