While it is true patterns suggests no hardware will be announced and a separate trailer is likely, be mindful our datapoints for this only go back to 2017, and all have been hardware revisions, not brand new hardware.
Until the Switch and post-Iwata direct established the current pattern, Nintendo was happy to mix hardware announcements in their usual E3 slot and the Switch's own late 2016 trailer concept reveal may have been driven in part by it's March release and less a desire to announce it separately. Move it up 3-4 months and the announcement would have lined up at E3.
The only strange about the June 29th timing is that Nintendo has all of this week and next week to themselves if they wanted to do a directt. Why they chose a late month slot and adjacent to financial briefing does make one wonder.
That said, we don't really know anything with regards to announcement timing and announcing something is like the last step in a very involved strategic planning and positioning of hardware. It's important, but probably has extra importance for us the public because that's the only bit we see.