err - the reason for Roman slavery was certainly not to provide labour for latifundia or provide a disincentive to industrialisation. Slavery had deep roots in Rome longe before there were latifundia, and not only in Rome (as IIRC Gaius said: "an institution contrary to natural law, but anchored in the law of the peoples (ius gentium)"). I doubt either the invention of a few gadgets (many of which would work just as well with slave labour) or a successful prevention of the depopulation of the Italic copuntryside by, say, the Gracchi would have done it.
First of all, both Hero and the Gracchi would be too late. If anything, slavery would have to be nipped at the inception of the Roman state (at the latest by the time of the XII Tables - if it makes it into those, the law stays on the books). The advantage is that you can basically invent any regional event you want freely to do it (we know almost nothing about that time other sthan little stories told by national mythographers), but the problem that it needs to be pretty convincing to let the Romans go against every single nation around them in this regard for centuries.
Then the issue of technology and slavery being opposed to each other - very unlikely. The Hellenistc Greeks pretty much invented the concept of 'technology', and they also invented industrial-grade chattel slavery. THe Islamic world around the year 1000 was pretty much as progressive as you get, and they had slavery written into their religious law. China had slavery throughout its history, and even Renaissance Italy and Portugal were slaveholding societies (as was, of course, the British empire until 1834 and the United states until 1863). It's a nice liberal myth, but as a general truth it doesn't wash.
I think a more realistic WI would be 'rome without mass slavery' frex. what if Rome had a law on the books that limited slavery to voluntary, punitive or hereditary status, but forbade enslavement of war prisoners? Admittedly, not really probably either, but that way the slaves pouring into Italy are only those taken as war booty and the few debt slaves, and not the populations of entire cities. Such a more limited labour pool would make the Republican latifundia impossible and require a different kind of social structure in the countryside. Given the stronger sense of civic pride and liberties, the colonate could not be developed the same way. Maybe an early development of labour contract law?