At the end of February, Isë Jingū announced the dates for the first large public events of the 63rd Shikinen Sengū, and this was reported in the 10th March issue of Jinja Shinpō.
The Mihishiroki Hōeishiki will take place on June 9th at the Inner Sanctuary and June 10th at the Outer Sanctuary. This is the “Honourable Hishiro Tree Pull Offering Ceremony”, and it involves trees being pulled into the precincts of the Inner and Outer Sanctuaries. These are (almost) the most sacred trees in the whole ceremony — the first to be felled, and the ones that are used closest to the goshintai.
The “hishiro” is the innermost container for the goshintai at both sanctuaries. The goshintai at the Inner Sanctuary is (reputedly) a large bronze mirror, said to be the one used to lure Amaterasu Ōmikami out of the Cave of the Heavens, and sent down with Ninigi-no-Mikoto to be venerated in the Imperial Palace until Yamatohimë-no-Mikoto brought it to Isë, at the request of Amaterasu Ōmikami herself, about two thousand years ago. Nobody seems to say anything about the goshintai of the Outer Sanctuary. Indeed, I only have a vague memory of reading somewhere that it is also thought to be a mirror. Of course, neither is ever on display.
While the pulling itself is public, it is highly traditional, and I believe that the basic rule is that these trees are only pulled by residents of the traditional areas, and probably by people whose ancestors have lived there for generations. (Later ceremonies, for less sacred trees, do invite wider participation.) However, there is also a tradition of welcoming and seeing off the trees on their way to Jingū. I do not know whether this simply involves waving at the trucks as they go past, but there are plans to do this with as much pomp as possible. It happens in Nagano, Gifu, Aichi, and Mië Prefectures, and those areas are accepting applications to participate.
So, if you live in one of those prefectures and would like to participate in the Shikinen Sengū from as early as possible, I recommend asking your local priest what is happening.