Another issue with adding WO to Steam is the monthly subscription would have to be more expensive if OneTooFree is to maintain current revenues per player as Steam takes a cut.
With regards to a marketing timeline, I don't think there is any necessity to have a published plan which customers can critique. I get why people want to know because a good PR / Marketing / Advertising strategy can lead to increased numbers of players which improves the enjoyment of the game for everyone. With a competent plan it will also generate a Return on Investment which would further improve development resources, so it's clear why customers want that information. I just don't think it is necessary and most companies will not release internal business strategy documents like that.
Wurm in particular has always had an issue with PR and Marketing which has always stemmed from confidence in the game among the leadership. This is not to denigrate the game or current and former leaders, but all too often there was a fear of too much exposure of the game because it was "not ready" or "not until x feature is implemented". This always pushed back my own plans for Wurm PR / Marketing / Advertising while I was assisting in this area some years ago.
If I would offer my 2 iron, and this is only intended as advice not as criticism, and you will agree I am making constructive suggestions here, I would urge a press strategy first and foremost. If Wurm has someone internally who has formal experience working with the press, get them to write press releases and to develop a relationship with journalists in the gaming world. Some of the very biggest spikes in Wurm population have been as a result of positive press coverage, which is free to achieve if you are sending out press releases. I can tell you this for a fact.
I have a good very recent example. The cooking stuff is great and is certainly something Wurm needs to shout about. Yet it seems there was no attempt to gather press coverage except by a player - Milosanx - which led to it being covered in Massively Overpowered. The credit is at the bottom and information was gathered from the forums. Really they should have had a Press Release to work from, along with every other games website we could list.
I think this is particularly important given some parts of Wurm are dead and intermittent coverage led by gaming magazines, such as when I was approached by RPS this month, allows those magazines to set the narrative, or at least not know that the one particular server I was on is an exception to the rule - Wurm is not dying. But those journalists can only know that if you tell them in the form of press releases.
Marketing involves analysing a lot of data (which we do have) about audience and customer habits and it would be worth the team looking into but again it requires a little experience. Advertising follows on from Marketing, where you specifically target audiences with advertising campaigns based on your marketing research.