(Regression) Node module resolution does not respect package.json in sub-folders

[Seikho]

TypeScript Version: 2.5.3 / next

Code

See a minimal repro at https://github.com/seikho/resolution-repro

Importing from module/sub-folder returns a compiler error when no index.ts is present despite a package.json with a valid typings property being present.

// Should work when node_modules/mod/mod-a contains a package.json with "typings" property
import { add } from 'mod/mod-a'

// A workaround will work however
import { add } from 'mod/mod-a/src'

Expected behavior:
Should compile okay

Actual behavior:
Fails to compile with error TS2307: Cannot find module 'mod/mod-a'

[Seikho]

Is there a reason this is in the 2.7 milestone instead of in the next version/patch?