Could be a minor lineage but it can not be Proto-Thracian cause it didn't formed the bulk of the population from the sources we have now,and was most probably not associated with speakers of Thracian language.
This R1b is out of historical Thracian lands,Thracians expanded to Panonia and Southern Poland,Ukraine,river Dniester and Moldova and elsewhere in Balkans but in bit later times than 2700 B.C when this R1b is found in Croatia.
So please when you write your own theories like Bastarnae were I2a din or something similar,say that that is your own opinion like i do,or quote a scholar if you mention one.
No. You can read about proto-Thracians:
https://en.wikipedia.org/wiki/Dacians#cite_note-61
Evidence of proto-Thracians or proto-Dacians in the prehistoric period depends on the remains of material culture. It is generally proposed that a proto-Dacian or proto-Thracian people developed from a mixture of indigenous peoples and Indo-Europeans from the time of Proto-Indo-European expansion in the Early Bronze Age (3,300–3,000 BC)[60] when the latter, around 1500 BC, conquered the indigenous peoples.[61] The indigenous people were Danubian farmers, and the invading people of the BC 3rd millennium were Kurgan warrior-herders from the Ukrainian and Russian steppes.[62]
[60] Hoddinott, p. 27.
[61] Casson, p. 3.
[62] Mountain, 1998, p. 58
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About origin of I-CTS10228 everyone can give own views, and readers are judging. We had long journey in this thread until member Sile introduced Bastarnae. In other genealogy forums about Bastarnae as carriers of I-CTS10228 written a lot, earlier. It is not easy terrain for coming to knowledge, and mostly forums about genealogy write about it. You can find another view which gave Tomenable who thinks I-CTS10228 emerged in Polesia. We will find in scientific papers when scientists investigate some territory and period and reveal findings.