The concerns are based on my own end-user experience with touch applications (both native and web SPA). Even slim and clean UIs may be prone to the same problem - the learning curve is gradual than desktop. It is always trial-and-error because there's no mouse to hover.

Despite the wishful thinking, graphic UI elements fail the expectations - no matter how good the icons are, it is not enough. And to be honest, fancy font-faced, lazy-bottomed flat icons aren't very good at explaining things.

The problem primarily affects smaller touch screens that don't have extra space for labels. But even big screens cannot afford explanatory i18zed labels on everything.

I'm considering two possibilities to improve UX of touch screens UIs.

Long press (all) / force touch (iOS)

This is the first thing I'm trying as a user to get a clarification on UI element because this is the only thing available to respectable hand-owner that has a chance to not perform undesirable actions.

In practice, this behaviour is very poorly supported (at least on devices that don't do 3D touch), to the point where it can be considered counter-intuitive.

Help-mode switch

When 'help' mode is triggered with big red 'wth?!' button it can significantly lower the barrier to entry, especially in larger apps (much better than welcome tour in my experience).

The major problem with it is that there's no extra space on the bar. Moving the button to overflow menu (Android) would harm the accessibility, and moving 'help' mode switch to settings renders it practically useless.

Another problem is the layout. It may be painful to maintain a separate one for the mode.

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I hope that the explanation is specific enough to ring a bell or two.

How do UX/UI guidelines cover this problem?

Are there acclaimed web or app implementations of the mentioned concepts? Do the other solutions exist?

Have 3D Touch affected UX trends and user habits in this context since its appearance?

A couple of illustrative examples may also help (in tech aspect I'm particularly interested in how this can be handled in common web UIs - Ionic & Material implementations, Bootstrap plugins).