One of Ko Wen-je's first moves after being elected mayor of Taipei was declaring support for a Nangang to Keelung MRT line, as part of a plan to build "youth housing" in Keelung. Although extending the MRT to Keelung seems to make sense and appears to be popular in Xizhi and Keelung, it hasn't gone anywhere- and for good reason.
For one thing, the route is already served by the TRA. Yes, the MRT is a good deal more pleasant and better-run, but given that MRT is supposed to stop at least once every two kilometers it's hard to see how it could be as fast as the TRA, even allowing for lower headways. What's more, the TRA is already slower than freeway buses, at least during off-peak.
There's also the question of demand: it isn't clear that enough people want to travel between Keelung and Taipei to justify an additional rail line. Even Keelung Station doesn't get a whole lot of ridership, with 6.5 million rides last year- about the same as Yingge and far fewer than Shulin, Taoyuan or Zhongli. Except for Songshan all the other stations between Taipei and Keelung have even fewer passengers.
Even if we assume there is sufficient unmet demand, the case for a new MRT line isn't obvious. Increasing capacity on the TRA could be sufficient, and would avoid the steep price tag of a whole new MRT line. The government has already taken some steps to do this, by adding a third track to a section of the TRA line near Nangang, but there are still only 11 trains per direction during rush hour- far fewer than many other similar rail systems manage in other countries. Longer trains could also be considered, as well as larger doors and level boarding to speed passenger flow and shorten dwell times. If capacity really does hit a maximum, perhaps it would be possible to add even more 3-track segments, 3-track the whole line, or rebuild curvy sections to shorten travel time. This would be expensive, but it would presumably still be cheaper than a whole new MRT line, and would provide much better connectivity with the rest of the TRA system. Turning lanes on the freeway into bus-only lanes could also increase the transportation capacity between Taipei and Keelung.
If bus lanes and upgrading the TRA isn't enough, then an MRT line would make sense- but not for bringing people from Keelung to Taipei. An MRT line could provide local, short distance service, with connections to major TRA stations providing transfers to TRA trains, which would provide express service. Such a line could probably terminate at Wudu or at the farthest Baifu, beyond which there simply aren't that many people until you get to downtown Keelung. Ideally the Bannan Line would be extended, though the current government claims that any Bannan Line extension would be blocked by the TRA and HSR and would therefore be impossible. Alternatives include extending the as-yet-unbuilt Minsheng-Xizhi Line, as the KMT appears to favor, or extending the Neihu Line. Ko and Keelung mayor-elect Lin Yu-chang seem to prefer starting a new line from Nangang, though that would force everyone bound for Taipei to transfer and make such a line less appealing than the TRA.
Even if there is too much demand for any of the above ideas to handle, then a whole new express line could be considered- but an MRT line, as it is defined in Taiwan right now, would probably still be too slow to compete with current options.
Although it's great that the Taiwanese electorate is still supportive of MRT, the government should still only build it when it's actually appropriate. There should also be a concerted effort to improve the TRA, which is all too often treated as a tourist attraction, rather than as the serious transportation system it is for hundreds of thousands, and could be for hundreds of thousands more.