Why the term Slavic migrations? When talking about Germanic, Anglo-Saxon or Indo-European it's expansions? The term Slav for the most part is not really a race or ethnicity or country it's a linguistic identity just like Germanic, Anglo-Saxon, or Indo-European or whatever. But where Slavic languages expanded it can only be a migration? I smell double standards there.
As far as I2a-Din for now it does seem very plausible it might have come to the Balkans carrying the Slavic language. But again it becomes very sketchy when labeling a hg to one linguistic group, as it's obvious there are many R1a carriers who don't speak a Slavic language as there are I2a-Din like Romanians who don't speak a Slavic language.
So I don't agree with handling this question as its just Slavic migrations. It sounds very black and white and simplistic and usually it's people who aren't Slavic that are content with that opinion, rather than it being the "objective" opinion.
Because unfortunately everything what is related for the Balkans is politics.
Science, scientific evidence, even common sense, does not help.
For example I read transcripts between Communist friends, comrade Stalin and comrade Enver Hoxha, how they agreed that Albanians are descendant of Ilyrians what Stalin loved especially after dissolution with Tito.
Communists were projected all areas of life and especially they loved to re-tailor history, archeology, anthropology etc.
Unfortunately nothing changed in the Balkans even today.
Politics is often more important than scientific facts and evidence.
For example Russian experts point out that I-CTS10228 is Slavic marker. It can be related with any evidence but you can notice that Russians generally prefer it because if carriers of I-CTS10228 are Slavic origin Russia can have big influence on population in that region, if no, this influence can be much smaller. What is more important science or politics in this case?
About TMCRA, there are eight and more different methods and they give different results. But hobbyists Nordtvedt and Klyosov get very similar result. I will not speculate about their result.
But we have two samples I-CTS10228* one is from Poland but one is from Alsace (France-Germany border). What does that say? Were I-CTS10228 carriers in wider European areas (where dominated R1a or R1b carriers, or I2a carriers themselves)? Where we can find third I-CTS10228*, in Austria, Slovenia, Croatia, Hungary, Serbia... We don't know, only can speculate. And if we see older brother I-FGC20479 he is found in British isles. I-CTS10228, I-FGC20479, and related clades (we can go to ancestor I-P37 if you want) are everywhere in Europe.
What is interesting because above mentioned clades were in the wider European areas their carriers were been associated with other expansions, for example Goths. I comment this with one Russian expert but he rejected that argument, he prefers that E-V13 carriers are related with Illyrians and I2a carriers with Slavs (Russians embrace Albanian speculations but new studies mainly by Western scientists give totally different picture). Regardless of his expertise (Russian scientists participate in many world top genetic genealogy research and publish alone or a part of a world expert teams in prominent international journals what is logical because of developed science and Russia and a lot of Institutes) I ask myself if his attitude is very trivial and unscientific, if it is really science or politics has a connection.
It will be many new findings and new studies and we will know better. Therefore better not to speculate. Really I would like if it is possible to determine which haplogroups belonged to the Roman emperors of Illyrian origin and members of upper classes Illyrian origin in the Balkans in the Roman epoche.
Illyrians dissapeared as political entity probably in 2-4 century and their language dissapeared because they are Romanised (according scientific evidence, especially newer studies, Albanian nothing to do with Illyrian) but with new samples we will have more knowledge about their genetics.
Someone should not be surprised if it varied by regions and if it changed with time.