There was formerly a respectable tradition (17–19c) of using the apostrophe for noun plurals, especially in loanwords ending in a vowel (as in We doe confess Errata's, Leonard Lichfield, 1641, and Comma's are used, Phillip Luckcombe, 1771) and in the consonants s, z, ch, sh (as in waltz's and cotillions, Washington Irving, 1804).
Although this practice is rare in 20c standard usage, the apostrophe of plurality continues in at least five areas:
- With abbreviations such as V.I.P.'s or VIP's, although forms such as VIPs are now widespread.
- With letters of the alphabet, as in "His i's are just like his a's" and "Dot your i's and cross your t's." In the phrase do's and don'ts, the apostrophe of plurality occurs in the first word but not the second, which has the apostrophe of omission: by and large, the use of two apostrophes close together (as in don't's) is avoided.
- In decade dates, such as the 1980's, although such apostrophe-free forms as the 1980s are widespread, as are such truncations as the '80s, the form the '80's being unlikely.
- In family names, especially if they end in -s, as in Keeping up with the Jones's, as opposed to the Joneses, a form that is also common.
So there are 300+ years of tradition of 's for plural forms of non-words, and about 20 years without. I suspect the internet has much to do with this as it has decimated proper punctuation from the English language in many contexts (texting, tweeting, IM'ing, etc.). I would write 1000's of uses and not 1000s of uses. It's the convention I was taught growing up, although it seems most of the major style guides have since abandoned it.
You said it yourself, "BMW 335is" is confusing. We have five BMW 335i's on the lot. I feel there is no confusion with possessive there. The point of punctuation is to lend clarity. Non-words don't have innate plural forms, and possessive is always easy to tell from context. And when you start to stack structures you usually have options:
"We have five BMW 335is' mufflers." "We have the mufflers from five BMW 335i's."