I have no love for Splinter Twin. The combo with Deceiver Exarch to produce infinite tokens for the kill pushed me out of playing Standard until its eventual rotation from the format. It also kept me from exploring modern in the early days of the format. But even I have to admit that Modern has gained a great many answers to kill the combo either before or as it's about to happen. Urza Tron and Affinity have become better decks overall.
I realize that it seems stupid to ban a card like Splinter Twin that was just reprinted in Modern Masters 2015. At this point, twin decks are more of a nuisance than an oppressive force in the format. This is good news though for Chord of Calling type decks that focus on using a similar combo with Kiki-Jiki, Mirror Breaker. The combo is more fragile because of being based off of a 2 toughness creature rather than an enchantment and a 4 toughness creature in the Exarch.
What Wizards is really doing is getting rid of two nuisances. Summer Bloom at this point was an enabler for a deck that just had been running all over the format as of late and probably well deserved being stopped in its tracks. It also doesn't hurt my feelings to see my least favorite Modern legal card bounced from the playing field. What this does is help some lower tier decks that may have had a bad matchup against Splinter Twin and Amulet Bloom more of a chance.
The other effect is the decent sized minority that stayed out of Modern because they remember Splinter Twin bouncing them out of tournaments again and again. Modern is a big money machine for Wizards right now and they want to get all the players into it that they can. They just waited too long to ban Twin. But you'll never see me mad about it.