De-retroflexion of ‹zh, ch, sh, r› is apparently
very widespread in mainland China. The entirety of
Southwestern Mandarin is usually described like this (having ‹z, c, s› and an English [z] sound as in "zipper" instead). I actually have access to some survey of Mandarin dialects so I'll try to get you more info later.
Alright, I looked at Margaret Mian Yan's
Introduction to Chinese dialectology (Lincom Europa: München (Germany), 2006), where she presents a survey of the dialects of a number of Chinese cities. For reasons I don't understand completely, she doesn't provide information for all of them consistently, sometimes mentioning some (e.g. Qīngdǎo) and sometimes omitting them. At least for our question here, she does provide data for all of: Běijīng, Jǐnán, Yāntái (Shandong), Nánjǐng (Jiangsu), Tàiyuán (Shanxi), Xī'ān (Shaanxi), Lánzhōu (Gansu) and Chéngdū (Sichuan). Also, for obvious reasons I can't just give you the tables...
Since we're basically comparing Beijing Mandarin with the others:
Beijing sh, if coming from Middle Chinese /書 *ɕ, 熟 *ʑ/, is pronounced as [f] in Xī'ān and Lánzhōu, and [s] in Yāntái, Tàiyuán and Chéngdū ([ʂ] in the others). If Beijing sh comes from Middle Chinese /師 *ɕ/, then it's pronounced [s] in Tàiyuán, Xī'ān and Chéngdū.
Beijing r is pronounced as [z] in Chéngdū and Tàiyuán; dropped altogether in Yāntái; sometimes pronounced as [l] in Jǐnán, [v] in Xī'ān and Lánzhōu ([ʐ] elsewhere, it doesn't account for [ɻ] for some reason).
Beijing zh is pronounced [ts] in Yāntái (though here also [tɕ] if coming from MC /知 *ʈ/) Chéngdū and Tàiyuán.
Beijing ch is pronounced [tsʰ] in Yāntái, Chéngdū and Tàiyuán; if coming from MC /初 *tʃʰ/ also [ts] in Yāntái, and [pf] in Lánzhōu and sometimes Xī'ān,.