Analysis and speculation:
Title:
Touhou Kishinjou - Castle of Shining Needles
Kishin = oni gods from hell, like the one who tried to assassinate Seiga in WaHH. Needle mountain is an important feature of hell, referenced by Remilia and Orin's spell card, and mentioned very recently in FS Chapter 1. The hint is too blatantly obvious, must be a trap.
The symbol in the game logo looks sort of like a modern tatoo. With Sakuya, the Western-style mirror frame in title screen, the logo, and a boss wearing a red cape, the game's tone feels a bit more Western than recent games.
Needless to say, this is like MoF, another back-to-basic game with a revamped engine. Note that ZUN calls EoSD a "20th Century-Extending Game of 21th Century" (see its cover). Now he's doing "2000s Neo-Retro".
Pre-game:
It sounds like each character will have two choices: "[use possessed weapon and] struggle against the weapon in one's own hands", and "abandon weapon". As shown in the screenshots, the Mini-Hakkero has become corrupted, and can be used as a flamethrower.
People have pointed out Reimu's gohei stick kept getting longer with each game. It's even longer now.
Normal mode is "for all ages", so Easy is "for children", Hard is "for adults", and Lunatic is probably "for long-living youkai".
Stage and season:
In what appears to be the 1st stage... Reimu shouldn't have dialogue before the game starts, so her zero score must be the result of debugging.
The stage is a road with water on its left side, pebbles and willows on its right side. The story should take place in summer. Previously summer was occupied by fighting games, but with HM taking place in spring, summer is free again.
Story:
The peaceful youkai are rebelling, so maybe the TD Extra title is a preview of that. Or it's a preview for both HM and DDC.
It's also interesting to see ZUN use the word 大人 again in the story synopsis. It's literally "like an adult", meaning "docile, quiet". You can see it a whole lot in the IaMP story.